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Number and Letter Series for CUET General Aptitude

About 10 min to learn · 68 questions

A series question gives a few terms that follow one hidden rule and asks for the next term, a missing term, or the one term that breaks the rule. The rule is almost always simple; what costs time is testing rules in a random order. This lesson gives a fixed order of tests for number series, the squares, cubes and primes to know, alternating series, letter positions and opposite letters, alphanumeric series, repeating patterns and wrong terms, with worked examples and traps.

Syllabus area
Logical and Analytical Reasoning
On this page · 8 sections
  1. 01The core idea
  2. 02Number series
  3. 03Letter series
  4. 04Patterns and wrong terms
  5. 05Exam shortcuts
  6. 06Common mistakes
  7. 07Quick revision
  8. 08Check your understanding

The core idea

Test rules in a fixed order and stop at the first one that fits every term: differences, then ratios, then squares and cubes, then two interleaved series. Random guessing is what costs time; the rules themselves are simple.

Letters are numbers in disguise. Turn each letter into its position, A = 1 to Z = 26, solve the number series, and turn the answer back.

Number series

How do you find the rule in a number series?

Work through the tests in order and check the rule on every term, not just the first two.

  1. Differences. If the gaps are constant, add a fixed step; if the gaps form a pattern, continue it.
  2. Ratios. For fast growth, divide each term by the one before: a ratio of about 2 or 3 usually means ×2±k\times 2 \pm k or ×3±k\times 3 \pm k.
  3. Squares and cubes. Compare terms with the nearest square or cube.
  4. Alternating. If terms rise and fall, split them into odd and even places.
  5. Special sequences. Primes, the sum of the two before, and a multiplier that grows.

Example 1 · Growing differences

Find the next term: 9, 14, 24, 39, 59, ?

  1. Differences: 5, 10, 15, 20, rising by 5.

  2. Next difference 25: 59+25=8459 + 25 = 84.

Answer

84

What if the differences are not constant?

Take differences of the differences. If those are constant, the step grows steadily, often a square pattern in disguise. If the differences double or triple, the rule is ×2±k\times 2 \pm k or ×3±k\times 3 \pm k.

Differences look likeRule to tryExample
Constant: 4, 4, 4Add a fixed number3, 7, 11, 15
Rising by a constant: 3, 5, 7Squares ±k\pm k2, 5, 10, 17, which is n2+1n^2 + 1
Doubling: 2, 4, 8×2±k\times 2 \pm k3, 5, 9, 17, which is ×2−1\times 2 - 1
Tripling: 2, 6, 18×3±k\times 3 \pm k2, 4, 10, 28, which is ×3−2\times 3 - 2
Squares: 1, 4, 9Third differences constant5, 6, 10, 19
Equal to earlier termsSum of the previous two2, 5, 7, 12, 19

Example 2 · Doubling differences

Find the next term: 6, 11, 21, 41, 81, ?

  1. Differences: 5, 10, 20, 40, doubling, so the next is 80 and the term 81+80=16181 + 80 = 161.

  2. As one rule: ×2−1\times 2 - 1, and 81×2−1=16181 \times 2 - 1 = 161. Both views agree.

Answer

161

Which squares, cubes and primes should you know by heart?

Squares to 25225^2, cubes to 12312^3 and primes to 100. A series that almost fits one of these lists is the commonest hard question, and you cannot spot it if you have to work the list out first.

ListValues
Squares1, 4, 9, 16, 25, 36, 49, 64, 81, 100, 121, 144, 169, 196, 225, 256, 289, 324, 361, 400, 441, 484, 529, 576, 625
Cubes1, 8, 27, 64, 125, 216, 343, 512, 729, 1000, 1331, 1728
Primes2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97

Exam shortcut

Common variations: n2±1n^2 \pm 1, n3±1n^3 \pm 1, n2+n=n(n+1)n^2 + n = n(n + 1), n3−nn^3 - n, squares of primes (4, 9, 25, 49, 121), and squares with an alternating sign.

How do you solve an alternating (interleaved) series?

Split the series into the terms in odd places and the terms in even places, solve each separately, and decide which half the asked term belongs to: the 7th term continues the odd places, the 8th the even.

Example 3 · Two series in one

Find the next term: 5, 26, 7, 23, 9, 20, ?

  1. Odd places: 5, 7, 9, rising by 2. Even places: 26, 23, 20, falling by 3.

  2. The 7th term is an odd place: 9+2=119 + 2 = 11.

Answer

11

The even series would give 17, exactly the kind of wrong option you will see.

Key idea

Some alternating series use two operations in turn, such as ÷2\div 2 then ×3\times 3. Write the operation between every pair of terms and the alternation shows.

Letter series

How do you find letter positions quickly?

Turn every letter into its position and solve the number series. The EJOTY trick gives anchors: E, J, O, T and Y are 5, 10, 15, 20 and 25, and every other letter is at most two steps from one.

ABCDEFGHIJKLM
12345678910111213
NOPQRSTUVWXYZ
14151617181920212223242526

Example 4 · A letter series

Find the next letter: F, I, M, R, ?

  1. Positions: 6, 9, 13, 18, with jumps 3, 4, 5.

  2. Next jump 6: 18+6=2418 + 6 = 24, which is X.

Answer

X

Exam shortcut

A letter's position from Z is 27 minus its position from A: M is 13th from A and 14th from Z. Letter series use the same rules as number series: a fixed jump (B, E, H, K), doubling positions (A, B, D, H, P), squares (A, D, I, P, Y) and primes (B, C, E, G, K, M).

What are opposite letters, and where do they appear?

Opposite letters are pairs whose positions add to 27: A–Z, B–Y, C–X, and so on to M–N in the middle. They appear in pair series like AZ, BY, CX and in many coding questions.

A–ZB–YC–XD–WE–VF–UG–TH–SI–RJ–QK–PL–OM–N

Example 5 · A pair series

Find the next pair: CX, EV, GT, ?

  1. First letters C, E, G jump by 2, so the next is I, position 9.

  2. Each second letter is the opposite of the first: 27−9=1827 - 9 = 18, which is R.

Answer

IR

Exam shortcut

In a group series, treat each column as its own series. In AZY, BXV, CVS the first column moves +1, the second −2 and the third −3, and the answer must satisfy every column.

How do you solve letter-number (alphanumeric) series?

Split each term into its letter part and number part and solve each separately. Often the number is tied to the letter's position, which gives a built-in check.

Example 6 · Letters and numbers

Find the next term: B3, E6, H9, ?

  1. Letters B, E, H: positions 2, 5, 8, jumping 3, so the next is K, 11.

  2. Numbers 3, 6, 9: +3, so the next is 12.

Answer

K12

Watch out

In a long arrangement of letters, digits and symbols, convert positions to one number first: 5th to the right of the 9th from the left is the 14th from the left. If some elements are removed, rewrite the shorter arrangement before counting.

Patterns and wrong terms

How do you complete a repeating letter pattern with blanks?

Find the length of the block that repeats, then fill every blank from it. Try block lengths of 3, 4, 5 and 6 until every shown letter agrees.

Example 7 · A repeating block

Fill the blanks: m n _ m n o _ n o m _ o

  1. Try a block of 3: mn_ | mno | _no | m_o. The block mno fits every shown letter.

  2. The blanks are o, m and n.

Answer

o, m, n, making mnomnomnomno

Exam shortcut

Mark the block boundaries before choosing, and read the filled string block by block: an option that fits three blanks but breaks the fourth is always offered. Some blocks read the same both ways, such as pqrrqp.

How do you find the wrong term in a series?

Find the rule from the terms that agree, then test every term. A wrong term spoils two neighbouring differences, so look for the term shared by the two odd differences, and check that the term after it fits the corrected value.

Example 8 · The wrong term

Find the wrong term: 2, 5, 11, 23, 48, 95

  1. Differences 3, 6, 12, 25, 47: the first three double, then the pattern breaks.

  2. The rule is ×2+1\times 2 + 1: 2, 5, 11, 23, then 47, then 95.

  3. 95 fits after 47, so 48 is wrong.

Answer

48

Blaming 95 is tempting, since 48×2+1=9748 \times 2 + 1 = 97, but 95 is right after the correct value.

Key idea

A good wrong-term question has only one term that can change to make the series fit. For a missing term in the middle, find the rule from the complete stretch, fill the gap, and check the term after it.

Exam shortcuts

  • Fixed order. Differences, ratios, squares and cubes, alternating, special.
  • EJOTY. 5, 10, 15, 20, 25 anchor every letter.
  • 27. Opposite letters, and position from Z.
  • Split. Odd and even places, letters and numbers, columns.
  • Check every term. Two terms fit many rules.

Common mistakes

  • Repeating the last difference when the differences grow.
  • Forgetting the ±k\pm k. ×3\times 3 of the last term is always an option.
  • The wrong half of an alternating series.
  • Stopping after two terms. 2, 4 fits both +2 and ×2\times 2.
  • Counting letters, not jumps. B to E is a jump of 3.
  • Off by one in positions. 5th to the right of the 9th is the 14th.
  • Blaming the term after the wrong one.
  • Ignoring a simpler rule. If a constant difference fits, the examiner meant it.

Quick revision

Number series

  • Differences, then second differences
  • Doubling differences: ×2±k\times 2 \pm k
  • Near squares or cubes: n2±kn^2 \pm k, n3±kn^3 \pm k
  • Rising and falling: split odd and even places

Letters

  • A = 1 … Z = 26, EJOTY anchors
  • Opposites add to 27
  • From Z = 27 − from A

Patterns

  • Repeating block: try lengths 3 to 6
  • Wrong term spoils two differences
  • Check the term after it

Letter positions and opposite letters do most of the work in coding and decoding, and number and letter pairs follow the same rules in analogies and classification.

Next · 07Quick revision

Check your understanding

68 questions, grouped by type, easy to hard. Pick an answer and check it. The worked solution opens when you ask for it.

Number seriesQ1 of 68Q1

Number series

22 questions

Which number comes next in the series 7, 12, 17, 22, 27, ?

Options for question 1

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AnswerA · 32

  1. Differences: 12−7=512 - 7 = 5, 17−12=517 - 12 = 5, 22−17=522 - 17 = 5, 27−22=527 - 22 = 5.

  2. The difference is always 5, so the next term is 27+5=3227 + 5 = 32.

Worth noting

37 adds 10, which is the jump across two terms, not one.

Find the next term of the series 5, 15, 45, 135, ?

Options for question 2

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AnswerC · 405

  1. The differences 10, 30, 90 are not constant, so try ratios: 15÷5=315 \div 5 = 3, 45÷15=345 \div 15 = 3, 135÷45=3135 \div 45 = 3.

  2. Each term is 3 times the one before, so the next term is 135×3=405135 \times 3 = 405.

Worth noting

180 adds the last difference (45) instead of multiplying, and 270 doubles instead of tripling.

What should replace the question mark in 11, 14, 20, 29, 41, ?

Options for question 3

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AnswerC · 56

  1. Differences: 3, 6, 9, 12. They go up by 3 each time.

  2. The next difference is 15, so the next term is 41+15=5641 + 15 = 56.

Worth noting

53 repeats the last difference, 12. The differences are themselves a series and must be continued.

Choose the number that comes next: 4, 7, 12, 19, 28, ?

Options for question 4

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AnswerD · 39

  1. Differences: 3, 5, 7, 9, rising by 2, so the next difference is 11.

  2. Next term =28+11=39= 28 + 11 = 39. Check: the terms are 12+3,22+3,32+3,42+3,52+31^2 + 3, 2^2 + 3, 3^2 + 3, 4^2 + 3, 5^2 + 3, and 62+3=396^2 + 3 = 39.

Worth noting

36 is 626^2 without the +3. 37 repeats the last difference, 9, and 38 adds 10, as if the differences rose by 1.

Which number continues the series 2, 3, 5, 7, 11, 13, ?

Options for question 5

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AnswerB · 17

  1. The terms are the prime numbers in order: 2, 3, 5, 7, 11, 13.

  2. The next prime after 13 is 17 (14, 15 and 16 all have factors).

Worth noting

15 is odd but not prime (15=3×5)(15 = 3 \times 5). 19 skips 17, which is prime.

Find the missing next number: 4, 6, 9, 13, 18, ?

Options for question 6

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AnswerB · 24

  1. Differences: 6−4=26 - 4 = 2, 9−6=39 - 6 = 3, 13−9=413 - 9 = 4, 18−13=518 - 13 = 5.

  2. Each difference is one more than the last, so add 6: 18+6=2418 + 6 = 24.

Worth noting

23 repeats the difference 5.

Which number comes next in 2, 2, 4, 12, 48, ?

Options for question 7

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AnswerD · 240

  1. Ratios: 2÷2=12 \div 2 = 1, 4÷2=24 \div 2 = 2, 12÷4=312 \div 4 = 3, 48÷12=448 \div 12 = 4.

  2. The multiplier rises by 1 each step, so the next is 48×5=24048 \times 5 = 240.

Worth noting

192 multiplies by 4 again; the multiplier itself must grow.

What is the next number in the series 4, 9, 25, 49, 121, ?

Options for question 8

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AnswerB · 169

  1. The terms are 22,32,52,72,1122^2, 3^2, 5^2, 7^2, 11^2: squares of the prime numbers.

  2. The next prime is 13, so the next term is 132=16913^2 = 169.

Worth noting

144 is 12212^2, but 12 is not prime.

What number comes next in the series 3, 7, 15, 31, 63, ?

Options for question 9

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AnswerC · 127

  1. Test the gaps first: 4, 8, 16, 32. They are doubling, which suggests a multiplicative rule.

  2. Check it: each term is double the one before it, plus one. 3×2+1=73 \times 2 + 1 = 7, 7×2+1=157 \times 2 + 1 = 15, 15×2+1=3115 \times 2 + 1 = 31, 31×2+1=6331 \times 2 + 1 = 63.

  3. So the next term is 63×2+1=12763 \times 2 + 1 = 127.

Worth noting

The 126 on offer is simply double the last term and forgets the +1. Each term is also one less than a power of two: 4, 8, 16, 32, 64, 128.

What number comes next in the series 2, 6, 12, 20, 30, ?

Options for question 10

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AnswerC · 42

  1. The differences between consecutive terms are 4, 6, 8 and 10 — rising by 2 each time.

  2. The next difference is therefore 12, giving 30+12=4230 + 12 = 42.

  3. The rule can also be written directly: the terms are 1×21 \times 2, 2×32 \times 3, 3×43 \times 4, 4×54 \times 5, 5×65 \times 6, so the next is 6×7=426 \times 7 = 42.

Worth noting

When the first differences are not constant, take the differences again. Here they are a constant 2, which is the signature of a rule built on n(n+1)n(n+1).

What is the next term of the series 3, 5, 9, 17, 33, ?

Options for question 11

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AnswerC · 65

  1. Differences: 2, 4, 8, 16. They double, so the next difference is 32.

  2. Next term =33+32=65= 33 + 32 = 65.

  3. The same rule in one line: each term is 2×(previous)−12 \times (\text{previous}) - 1, and 33×2−1=6533 \times 2 - 1 = 65.

Worth noting

49 adds 16 again. 66 doubles 33 but forgets the −1.

Find the number that should come next: 2, 5, 14, 41, 122, ?

Options for question 12

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AnswerB · 365

  1. Test ×3\times 3: 2×3=62 \times 3 = 6, but the next term is 5, one less.

  2. So the rule is ×3−1\times 3 - 1: 5×3−1=145 \times 3 - 1 = 14, 14×3−1=4114 \times 3 - 1 = 41, 41×3−1=12241 \times 3 - 1 = 122.

  3. Next term =122×3−1=365= 122 \times 3 - 1 = 365.

Worth noting

366 forgets the −1 and 367 adds 1 instead. The differences (3, 9, 27, 81) tripling is the same rule seen another way: 122+243=365122 + 243 = 365.

Which number comes next in the series 2, 9, 28, 65, 126, ?

Options for question 13

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AnswerD · 217

  1. Each term is one more than a cube: 13+1=21^3 + 1 = 2, 23+1=92^3 + 1 = 9, 33+1=283^3 + 1 = 28, 43+1=654^3 + 1 = 65, 53+1=1265^3 + 1 = 126.

  2. Next term =63+1=216+1=217= 6^3 + 1 = 216 + 1 = 217.

Worth noting

216 is 636^3 without the +1, and 215 subtracts 1 instead. 190 adds 43=644^3 = 64 to 126, confusing the cube with the difference (the differences are 7, 19, 37, 61, 91). Numbers just above 8, 27, 64 and 125 are a strong hint of cubes.

What comes next in the series 4, 30, 9, 27, 14, 24, ?

Options for question 14

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AnswerA · 19

  1. The terms jump up and down, so split them into two series.

  2. 1st, 3rd, 5th terms: 4, 9, 14 (add 5). 2nd, 4th, 6th terms: 30, 27, 24 (subtract 3).

  3. The 7th term belongs to the first series: 14+5=1914 + 5 = 19.

Worth noting

21 is the next term of the second series (24−3)(24 - 3), but the 7th term is an odd place, so it continues the first series.

Find the next number: 3, 4, 7, 11, 18, 29, ?

Options for question 15

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AnswerC · 47

  1. Differences 1, 3, 4, 7, 11 do not follow an obvious pattern, but notice 3+4=73 + 4 = 7, 4+7=114 + 7 = 11, 7+11=187 + 11 = 18, 11+18=2911 + 18 = 29.

  2. Each term is the sum of the two before it, so the next is 18+29=4718 + 29 = 47.

Worth noting

40 adds the last difference (11) again, and 58 doubles 29. When the differences look like the series itself, test 'sum of the previous two'.

Which number should come next in the series 2, 3, 7, 16, 32, ?

Options for question 16

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AnswerD · 57

  1. Differences: 1, 4, 9, 16. These are 12,22,32,421^2, 2^2, 3^2, 4^2.

  2. The next difference is 52=255^2 = 25, so the next term is 32+25=5732 + 25 = 57.

Worth noting

48 repeats the difference 16, and 41 adds 323^2 again. 50 adds 18, as if the differences rose by 2; they rise by 3, 5, 7, so the next rise is 9.

Find the term that comes next: 7, 10, 16, 28, 52, ?

Options for question 17

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AnswerA · 100

  1. Differences: 3, 6, 12, 24. They double each time.

  2. Next difference =48= 48, so the next term is 52+48=10052 + 48 = 100.

  3. Check with the rule ×2−4\times 2 - 4: 52×2−4=10052 \times 2 - 4 = 100.

Worth noting

104 doubles 52 but forgets to subtract 4. 148 adds 96, which is the difference after next (48 doubled once too often).

Which number comes next in the falling series 120, 99, 80, 63, 48, ?

Options for question 18

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AnswerB · 35

  1. Differences: 21, 19, 17, 15, falling by 2, so the next difference is 13 and 48−13=3548 - 13 = 35.

  2. Check: the terms are 112−1,102−1,92−1,82−1,72−111^2 - 1, 10^2 - 1, 9^2 - 1, 8^2 - 1, 7^2 - 1, so the next is 62−1=356^2 - 1 = 35.

Worth noting

33 subtracts 15 again. 36 is 626^2 without the −1.

Identify the next term of the series 1, 2, 6, 21, 88, ?

Options for question 19

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AnswerC · 445

  1. Try a changing multiplier with a matching addition: 1×1+1=21 \times 1 + 1 = 2, 2×2+2=62 \times 2 + 2 = 6, 6×3+3=216 \times 3 + 3 = 21, 21×4+4=8821 \times 4 + 4 = 88.

  2. The next step is ×5+5\times 5 + 5: 88×5+5=440+5=44588 \times 5 + 5 = 440 + 5 = 445.

Worth noting

440 stops after the multiplication, and 441 adds 1 as in the first step. Both the multiplier and the number added grow together here.

Which number fits next in the series 2, 3, 10, 15, 26, ?

Options for question 20

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AnswerA · 35

  1. Compare each term with a square: 2=12+12 = 1^2 + 1, 3=22−13 = 2^2 - 1, 10=32+110 = 3^2 + 1, 15=42−115 = 4^2 - 1, 26=52+126 = 5^2 + 1.

  2. The +1 and −1 alternate, so the 6th term is 62−1=356^2 - 1 = 35.

Worth noting

37 is 62+16^2 + 1, which forgets that the adjustment alternates; 36 ignores it altogether. The differences (1, 7, 5, 11, 9) look irregular, which is the signal to compare with squares.

What comes next in the series 8, 4, 12, 6, 18, 9, ?

Options for question 21

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AnswerC · 27

  1. The terms go down, up, down, up, so look at the operations: 8÷2=48 \div 2 = 4, 4×3=124 \times 3 = 12, 12÷2=612 \div 2 = 6, 6×3=186 \times 3 = 18, 18÷2=918 \div 2 = 9.

  2. The operations alternate ÷2\div 2 and ×3\times 3. The next is ×3\times 3: 9×3=279 \times 3 = 27.

Worth noting

4.5 halves again, missing the alternation. 18 doubles 9. Seen as two interleaved series (8, 12, 18, 27 and 4, 6, 9), each is ×1.5\times 1.5, which gives 27 as well.

Find the next number in the series 2, 12, 36, 80, 150, ?

Options for question 22

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AnswerB · 252

  1. Split each term into a square times the next number: 2=12×22 = 1^2 \times 2, 12=22×312 = 2^2 \times 3, 36=32×436 = 3^2 \times 4, 80=42×580 = 4^2 \times 5, 150=52×6150 = 5^2 \times 6.

  2. So the 6th term is 62×7=36×7=2526^2 \times 7 = 36 \times 7 = 252.

  3. Check with differences: 10, 24, 44, 70 have differences 14, 20, 26 (rising by 6), so the next difference is 70+32=10270 + 32 = 102, and 150+102=252150 + 102 = 252.

Worth noting

246 repeats the second difference 26 instead of raising it to 32, and 294 swaps the roles (72×6)(7^2 \times 6). When the numbers grow faster than squares but slower than doubling, try n2×(n+1)n^2 \times (n + 1) or n3±nn^3 \pm n.

Letter series

17 questions

Which letter comes next in the series B, E, H, K, N, ?

Options for question 23

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AnswerA · Q

  1. Positions: B = 2, E = 5, H = 8, K = 11, N = 14.

  2. Each letter is 3 places after the one before, so the next is 14+3=1714 + 3 = 17, which is Q.

Worth noting

Count the jump, not the letters between: from B to E there are two letters in between but a jump of 3.

Find the letter that continues the backward series Z, X, V, T, R, ?

Options for question 24

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AnswerD · P

  1. Positions: Z = 26, X = 24, V = 22, T = 20, R = 18.

  2. Each step goes back 2 places, so the next is 18−2=1618 - 2 = 16, which is P.

Worth noting

O is one step back; the series skips one letter each time (Y, W, U, S, Q are the skipped ones).

What letter should replace the question mark in D, H, L, P, ?

Options for question 25

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AnswerD · T

  1. Positions: D = 4, H = 8, L = 12, P = 16, the multiples of 4.

  2. Next position =16+4=20= 16 + 4 = 20, which is T. (EJOTY: T is the 20th letter.)

Worth noting

Q, R and S come from counting three letters forward instead of a jump of four.

Which pair of letters comes next in the series AZ, BY, CX, DW, ?

Options for question 26

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AnswerB · EV

  1. First letters: A, B, C, D, moving forward one place, so the next is E.

  2. Second letters: Z, Y, X, W, moving back one place, so the next is V.

  3. Each pair is a letter with its opposite (the two positions add to 27). The next pair is EV.

Worth noting

VE has the right letters in the wrong order.

Choose the group of letters that comes next: ZYX, WVU, TSR, ?

Options for question 27

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AnswerC · QPO

  1. The alphabet is being written backwards in blocks of three: ZYX, then WVU, then TSR.

  2. The next three letters going backwards after R are Q, P, O, so the group is QPO.

Worth noting

QRS has the right letters but runs forwards. PON starts one letter too late.

Which letter comes next in the series A, C, B, D, C, E, ?

Options for question 28

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AnswerA · D

  1. The moves are +2, −1, +2, −1, +2 (A to C, C to B, B to D, D to C, C to E).

  2. The next move is −1, so the letter after E is D.

  3. Equivalently, the odd places read A, B, C and the next one is D.

Worth noting

F is the next letter of the other interleaved series (C, D, E), which belongs to the 8th place, not the 7th.

What letter comes next in the series A, C, F, J, O, ?

Options for question 29

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AnswerC · U

  1. Count the steps through the alphabet between consecutive letters: A to C is 2, C to F is 3, F to J is 4, J to O is 5.

  2. The steps are growing by one each time, so the next step is 6.

  3. O is the 15th letter, and 15+6=2115 + 6 = 21, which is U.

Worth noting

Writing the position numbers — 1, 3, 6, 10, 15 — turns a letter series into a number series. Those are the triangular numbers, so the next is 21.

What is the next letter in the series A, B, D, H, ?

Options for question 30

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AnswerD · P

  1. Positions: A = 1, B = 2, D = 4, H = 8.

  2. Each position doubles (the jumps are 1, 2, 4), so the next position is 16, which is P.

Worth noting

L (12) adds 4 again, and N (14) adds 6, treating the jumps as rising by 2. The jumps 1, 2, 4 double, so the next jump is 8.

Find the next letter: Y, W, T, P, K, ?

Options for question 31

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AnswerB · E

  1. Positions: Y = 25, W = 23, T = 20, P = 16, K = 11.

  2. The backward jumps are 2, 3, 4, 5, growing by one, so the next jump is 6.

  3. 11−6=511 - 6 = 5, which is E.

Worth noting

F repeats the jump of 5 (11−5=6)(11 - 5 = 6) and D jumps 7. Keep the growing jump growing by exactly one.

Which group of letters should come next in the series BDF, HJL, NPR, ?

Options for question 32

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AnswerB · TVX

  1. Inside each group the letters skip one: B, D, F; H, J, L; N, P, R.

  2. The groups start at B = 2, H = 8, N = 14, jumping 6 each time, so the next starts at 20, which is T.

  3. Skipping one letter each time from T gives T, V, X.

Worth noting

TUV keeps the start but forgets that the letters inside the group skip one.

What letter comes next in the series A, Z, C, X, E, V, ?

Options for question 33

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AnswerA · G

  1. Split the series: 1st, 3rd, 5th letters are A, C, E (forward by 2); 2nd, 4th, 6th are Z, X, V (backward by 2).

  2. The 7th letter continues the first series: after E comes G.

Worth noting

T is the next letter of the backward series (after V), which fills the 8th place.

Which letter continues the series A, D, I, P, ?

Options for question 34

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AnswerD · Y

  1. Positions: A = 1, D = 4, I = 9, P = 16. These are 12,22,32,421^2, 2^2, 3^2, 4^2.

  2. The next position is 52=255^2 = 25, which is Y.

Worth noting

The jumps 3, 5, 7 also show it: the next jump is 9, and 16+9=2516 + 9 = 25. U (21) and W (23) use smaller jumps.

Find the next letter of the series B, C, E, G, K, ?

Options for question 35

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AnswerB · M

  1. Positions: B = 2, C = 3, E = 5, G = 7, K = 11. These are the prime numbers.

  2. The next prime is 13, which is M.

Worth noting

The jumps 1, 2, 2, 4 look irregular; that is the signal to write the positions and test primes. O (15) is odd but not prime.

Which letter comes next in C, D, F, G, I, J, ?

Options for question 36

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AnswerA · L

  1. Positions: C = 3, D = 4, F = 6, G = 7, I = 9, J = 10.

  2. The jumps alternate +1, +2, +1, +2, +1, so the next jump is +2: 10+2=1210 + 2 = 12, which is L.

Worth noting

M adds 3. The pattern is 'take two, skip one': CD, FG, IJ, then L.

Which pair of letters comes next in the series AZ, CX, FU, JQ, ?

Options for question 37

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AnswerD · OL

  1. First letters: A = 1, C = 3, F = 6, J = 10. The jumps are 2, 3, 4, so the next jump is 5, giving 15, which is O.

  2. Second letters: Z, X, U, Q are the opposites of A, C, F, J (each pair of positions adds to 27).

  3. The opposite of O is 27−15=1227 - 15 = 12, which is L. The next pair is OL.

Worth noting

OK moves the second letter back 6 instead of using the opposite rule. NM uses a jump of 4 again.

Which letter pair should replace the question mark in AB, CE, FI, JN, ?

Options for question 38

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AnswerC · OT

  1. First letters: A, C, F, J (positions 1, 3, 6, 10), jumps 2, 3, 4. Next jump 5 gives O (15).

  2. Inside each pair the gap grows: A to B is 1, C to E is 2, F to I is 3, J to N is 4.

  3. So the second letter is 5 after O: 15+5=2015 + 5 = 20, which is T. The pair is OT.

Worth noting

OS keeps the gap at 4. Two separate rules are at work (between pairs and inside a pair), and each must be continued.

Find the group of three letters that comes next: AZY, BXV, CVS, ?

Options for question 39

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AnswerB · DTP

  1. Read each column separately. First letters A, B, C move forward 1: next D.

  2. Second letters Z, X, V move back 2: next T.

  3. Third letters Y, V, S move back 3: next P. The group is DTP.

Worth noting

DTQ moves the third letter back 2 instead of 3, copying the middle column's rule.

Letter-number and repeating patterns

13 questions

Which term comes next in the series A1, C3, E5, G7, ?

Options for question 40

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AnswerC · I9

  1. Letters: A, C, E, G skip one letter each time, so the next is I.

  2. Numbers: 1, 3, 5, 7 go up by 2, so the next is 9. Each number is the position of its letter.

  3. The next term is I9.

Worth noting

H8 moves one step instead of two.

What should replace the question mark in 2B, 4D, 6F, 8H, ?

Options for question 41

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AnswerA · 10J

  1. Numbers: 2, 4, 6, 8, so the next is 10.

  2. Letters: B, D, F, H are the 2nd, 4th, 6th and 8th letters, so the next is the 10th letter, J.

  3. The next term is 10J.

Worth noting

10I pairs the right number with the 9th letter. EJOTY gives J as the 10th letter at once.

Which set of letters, filled into the blanks in order, completes the repeating pattern a _ c a _ c a b _ a b _ ?

Options for question 42

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AnswerA · bbcc

  1. Look for a block that repeats. The visible letters fit the block abc: a_c | a_c | ab_ | ab_.

  2. Fill each block as abc: the blanks are b, b, c, c.

  3. The complete pattern is abcabcabcabc.

Worth noting

Check every blank against its block; bbca breaks the last block, which would read aba.

Study the arrangement below and answer the question.

K 7 @ R 3 E # 9 M U 2 % B 6 A & T 4 = H

In the arrangement, how many digits are immediately followed by a symbol?

Options for question 43

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AnswerC · 3

  1. Look at each digit and the element just to its right: 7 @, 3 E, 9 M, 2 %, 6 A, 4 =.

  2. The digit is followed by a symbol in 7 @, 2 % and 4 =, so the count is 3.

Worth noting

'Followed by' means the element on the right. Reading leftwards (the element before each digit) gives a different count.

Find the next term of the series Z1, X4, V9, T16, ?

Options for question 44

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AnswerD · R25

  1. Letters: Z, X, V, T go back 2 each time, so the next is R.

  2. Numbers: 1, 4, 9, 16 are 12,22,32,421^2, 2^2, 3^2, 4^2, so the next is 52=255^2 = 25.

  3. The next term is R25.

Worth noting

R24 treats the numbers as rising by 8 at the end (a miscount of the differences 3, 5, 7, whose next value is 9).

Which term continues the series C6, F12, I18, L24, ?

Options for question 45

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AnswerB · O30

  1. Letters: C, F, I, L are positions 3, 6, 9, 12, so the next is 15, which is O.

  2. Numbers: 6, 12, 18, 24 go up by 6 (each is twice its letter's position), so the next is 30.

  3. The next term is O30.

Worth noting

P30 and N30 get the number right but miss the letter by one; count positions (EJOTY: O is 15), do not count on your fingers.

Choose the term that comes next: P3, N6, L12, J24, ?

Options for question 46

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AnswerC · H48

  1. Letters: P, N, L, J go back 2 each time (16, 14, 12, 10), so the next is 8, which is H.

  2. Numbers: 3, 6, 12, 24 double each time, so the next is 48.

  3. The next term is H48.

Worth noting

H36 adds 12 to 24 as if the numbers rose by a constant. The differences 3, 6, 12 double, so the number doubles.

The letter pattern a a _ b a _ b _ _ a b _ is made by repeating one block. Which letters fill the blanks from left to right?

Options for question 47

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AnswerD · babab

  1. The pattern has 12 places. Try blocks of 4: aa_b | a_b_ | _ab_.

  2. The block aabb fits all the letters that are shown.

  3. Filling each block as aabb gives the blanks b, a, b, a, b, and the pattern aabbaabbaabb.

Worth noting

A block of 2 (ab) cannot be right: the pattern starts with two a's. Try the block length that makes every shown letter agree.

Fill the gaps so that the same group of letters repeats throughout: _ a a _ b a _ c b a a _. What are the missing letters, in order?

Options for question 48

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AnswerC · bcac

  1. Try blocks of 4: _aa_ | ba_c | baa_ read against the shown letters.

  2. The block baac fits: the first block needs b and c, the second needs a, the third needs c.

  3. So the blanks are b, c, a, c, and the pattern is baacbaacbaac.

Worth noting

bcaa ends the third block with a, so it would read baaa instead of baac. After filling, reread the whole pattern block by block.

Study the arrangement below and answer the question.

K 7 @ R 3 E # 9 M U 2 % B 6 A & T 4 = H

In the arrangement, which element is 5th to the right of the 9th element from the left end?

Options for question 49

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AnswerD · 6

  1. The 9th element from the left is M.

  2. 5th to the right of the 9th is the 9+5=149 + 5 = 14th element from the left.

  3. Counting: K 7 @ R 3 E # 9 M U 2 % B 6, so the 14th element is 6.

Worth noting

B is 4th to the right of M (the 13th) and A is 6th to the right (the 15th): off-by-one counts. Convert to one position number before counting.

A block of letters is written twice to make p q _ r q p _ q r _ q _. Which letters, taken in order, go in the blanks?

Options for question 50

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AnswerA · rprp

  1. The shown letters p q _ r q p suggest a block of 6 that reads the same backwards: pqrrqp.

  2. Check the second block: _ q r _ q _ must be p q r r q p, so its blanks are p, r, p.

  3. The blanks in order are r (first block), then p, r, p, giving rprp.

Worth noting

A mirror block (pqr then rqp) is a common design. rqrp puts q where the second block starts, which should be p.

Study the arrangement below and answer the question.

K 7 @ R 3 E # 9 M U 2 % B 6 A & T 4 = H

In the arrangement, how many letters are immediately preceded by a digit and immediately followed by a symbol?

Options for question 51

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AnswerB · 2

  1. First find the letters preceded by a digit: E (after 3), M (after 9), A (after 6).

  2. Now check what follows each: E is followed by #, M by U, A by &.

  3. E and A satisfy both conditions, so the count is 2.

Worth noting

M is preceded by a digit but followed by a letter, so it fails the second condition. Check both sides of every candidate.

Study the arrangement below and answer the question.

K 7 @ R 3 E # 9 M U 2 % B 6 A & T 4 = H

If all the symbols are removed from the arrangement, which element will be 6th from the right end?

Options for question 52

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AnswerA · B

  1. Removing @, #, %, & and = leaves: K 7 R 3 E 9 M U 2 B 6 A T 4 H.

  2. Counting from the right: H (1st), 4 (2nd), T (3rd), A (4th), 6 (5th), B (6th).

  3. So the 6th element from the right is B.

Worth noting

A is the 6th from the right in the original arrangement; the removed symbols shift the count. Rewrite the shortened arrangement before counting.

Wrong or missing term

16 questions

One number in the series 3, 6, 12, 24, 46, 96 does not fit the pattern. Which is it?

Options for question 53

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AnswerC · 46

  1. Each term looks like double the one before: 3×2=63 \times 2 = 6, 6×2=126 \times 2 = 12, 12×2=2412 \times 2 = 24.

  2. Then 24×2=4824 \times 2 = 48, not 46, and 48×2=9648 \times 2 = 96 matches the last term.

  3. So 46 is wrong; it should be 48.

Worth noting

96 is correct, because it is double the RIGHT value, 48. Check the term after a suspect as well.

Find the wrong term in the series 5, 11, 17, 23, 30, 35.

Options for question 54

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AnswerD · 30

  1. Differences: 6, 6, 6, 7, 5. The pattern is +6, broken at the fifth term.

  2. 23+6=2923 + 6 = 29, and 29+6=3529 + 6 = 35 fits the last term, so 30 is wrong (it should be 29).

Worth noting

A wrong term spoils TWO differences (here 7 and 5). The term shared by both odd differences is the culprit.

What is the missing number in the series 4, 8, ?, 32, 64?

Options for question 55

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AnswerA · 16

  1. Test the ratio: 8÷4=28 \div 4 = 2 and 64÷32=264 \div 32 = 2.

  2. So each term doubles: the missing term is 8×2=168 \times 2 = 16, and 16×2=3216 \times 2 = 32 checks.

Worth noting

20 is halfway between 8 and 32, which assumes a constant difference. The known terms double, so the gap is filled by doubling.

Which number fills the gap in 6, 11, ?, 27, 38, 51?

Options for question 56

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AnswerD · 18

  1. Use the complete end of the series: 38−27=1138 - 27 = 11, 51−38=1351 - 38 = 13. The differences rise by 2.

  2. Working back, the differences are 5, 7, 9, 11, 13, so the missing term is 11+7=1811 + 7 = 18.

  3. Check: 18+9=2718 + 9 = 27.

Worth noting

16 adds 5 again. Always check that the missing term also works with the term AFTER it.

Spot the term that breaks the pattern: 1, 3, 7, 10, 15, 21, 28.

Options for question 57

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AnswerA · 7

  1. The last three differences are 5, 6, 7 (10 to 15, 15 to 21, 21 to 28): they rise by one each time.

  2. The full pattern is +2, +3, +4, +5, +6, +7, so the third term is 3+3=63 + 3 = 6, not 7.

  3. With 6 in place: 1, 3, 6, 10, 15, 21, 28.

Worth noting

With 7 in place the differences are 2, 4, 3, 5, 6, 7. The two that break the steady rise (4 and 3) meet at 7.

In the letter series C, F, I, L, P, R, one letter is wrong. Which one?

Options for question 58

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AnswerC · P

  1. Positions: C = 3, F = 6, I = 9, L = 12, P = 16, R = 18.

  2. The jump is 3 each time, so after L (12) should come O (15), and then R (18) fits.

  3. P (16) is the wrong letter; it should be O.

Worth noting

Writing the positions turns the letter series into 3, 6, 9, 12, 16, 18, where the odd term is easy to see.

Which number is the odd one out in the series 1, 8, 27, 64, 124, 216?

Options for question 59

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AnswerD · 124

  1. 1, 8, 27, 64 and 216 are the cubes 13,23,33,43,631^3, 2^3, 3^3, 4^3, 6^3.

  2. The fifth term should be 53=1255^3 = 125, so 124 is wrong.

Worth noting

124 is close to 125 on purpose; know the cubes up to 103=100010^3 = 1000 by heart.

In the series 2, 5, 10, 17, 26, 38, 50, exactly one number is wrong. Find it.

Options for question 60

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AnswerD · 38

  1. The terms are one more than squares: 12+1,22+1,32+1,42+1,52+11^2 + 1, 2^2 + 1, 3^2 + 1, 4^2 + 1, 5^2 + 1, and the last is 72+1=507^2 + 1 = 50.

  2. The sixth term should be 62+1=376^2 + 1 = 37, so 38 is wrong.

Worth noting

The differences 3, 5, 7, 9 should continue 11, 13; with 38 they read 12, 12.

Which term of the series 4, 9, 19, 40, 79, 159 is incorrect?

Options for question 61

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AnswerB · 40

  1. Test ×2+1\times 2 + 1: 4×2+1=94 \times 2 + 1 = 9, 9×2+1=199 \times 2 + 1 = 19.

  2. Next should be 19×2+1=3919 \times 2 + 1 = 39, not 40; then 39×2+1=7939 \times 2 + 1 = 79 and 79×2+1=15979 \times 2 + 1 = 159 both fit.

  3. So 40 is the wrong term.

Worth noting

79 is not wrong even though 40×2+1=8140 \times 2 + 1 = 81: it follows the correct value 39. Judge each term from the rule, not from a wrong neighbour.

One term in the series 2, 3, 5, 8, 13, 21, 35, 55 is wrong. Identify it.

Options for question 62

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AnswerD · 35

  1. Each term is the sum of the two before it: 2+3=52 + 3 = 5, 3+5=83 + 5 = 8, 5+8=135 + 8 = 13, 8+13=218 + 13 = 21.

  2. Next should be 13+21=3413 + 21 = 34, and then 21+34=5521 + 34 = 55 matches the last term.

  3. So 35 is wrong; it should be 34.

In the series AZ, BY, CX, DV, EV, which pair does not follow the pattern?

Options for question 63

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AnswerA · DV

  1. First letters A, B, C, D, E move forward one place: all fine.

  2. Second letters should move back one place: Z, Y, X, W, V. The fourth pair has V instead of W.

  3. So DV is wrong; it should be DW (D and W are opposite letters: 4+23=274 + 23 = 27).

Worth noting

EV is right: E and V are opposites (5+22=27)(5 + 22 = 27). Test each pair against the opposite-letter rule.

What number should replace the question mark in 2, 7, 22, ?, 202, 607?

Options for question 64

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AnswerB · 67

  1. Test ×3+1\times 3 + 1 on the known terms: 2×3+1=72 \times 3 + 1 = 7, 7×3+1=227 \times 3 + 1 = 22.

  2. So the missing term is 22×3+1=6722 \times 3 + 1 = 67.

  3. Check it forward: 67×3+1=20267 \times 3 + 1 = 202 and 202×3+1=607202 \times 3 + 1 = 607.

Worth noting

66 triples 22 but forgets the +1; the check with 202 exposes it, since 66×3+1=19966 \times 3 + 1 = 199.

The series 3, 5, 7, 11, 13, 15, 19, 23 is meant to follow one rule. Which number is out of place?

Options for question 65

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AnswerC · 15

  1. The terms are the odd primes in order: 3, 5, 7, 11, 13, then 17, 19, 23.

  2. 15 is not prime (15=3×5)(15 = 3 \times 5); the prime between 13 and 19 is 17.

  3. So 15 is the wrong term; it should be 17.

Worth noting

The differences 2, 2, 4, 2, 2, 4, 4 look almost regular, which can mislead. With 17 in place they are 2, 2, 4, 2, 4, 2, 4, the gaps between consecutive primes.

Exactly one number in 7, 13, 25, 49, 97, 194, 385 breaks the rule. Which number is it?

Options for question 66

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AnswerC · 194

  1. Differences: 6, 12, 24, 48, 97, 191. The first four double, then the pattern breaks.

  2. The rule is ×2−1\times 2 - 1: 7→13→25→49→977 \to 13 \to 25 \to 49 \to 97, and next 97×2−1=19397 \times 2 - 1 = 193.

  3. Then 193×2−1=385193 \times 2 - 1 = 385 matches the last term, so 194 is wrong.

Worth noting

It is tempting to blame 385, because 194×2−1=387194 \times 2 - 1 = 387. But 385 is exactly right after 193. The term that spoils two differences is the wrong one.

Find the wrong number in the series 3, 20, 6, 17, 12, 15, 24, 11.

Options for question 67

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AnswerB · 15

  1. The terms rise and fall, so split them. Odd places: 3, 6, 12, 24 (doubling), which is consistent.

  2. Even places: 20, 17, 15, 11. The rule is −3: 20,17,14,1120, 17, 14, 11.

  3. So 15 is wrong; it should be 14.

Worth noting

Looking at the whole series at once, nothing looks off. Splitting into the two interleaved series shows the break in the second one.

Two terms are missing from the series 5, ?, 17, 29, ?, 65. Which pair of numbers fills the gaps, in order?

Options for question 68

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AnswerA · 9 and 45

  1. Only one difference can be read directly: 29−17=1229 - 17 = 12, a multiple of 4. Try differences that grow by 4.

  2. Try differences 4, 8, 12, 16, 20: 5+4=95 + 4 = 9, 9+8=179 + 8 = 17, 17+12=2917 + 12 = 29, 29+16=4529 + 16 = 45, 45+20=6545 + 20 = 65.

  3. Every known term fits, so the gaps are 9 and 45.

Worth noting

11 and 43 keeps the ends of the series right but gives differences 6, 6, 12, 14, 22 that follow no rule. Both gaps must fit one pattern at once.

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