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HCF & LCM · Question 40 of 63

Question 40

MediumOriginal question

What is the smallest number which, when divided by 6, 8 and 15, leaves a remainder of 2 in each case?

Options for question 40

Show the answer and explanation
CorrectNot quiteAnswer C

Correct answer: C

Explanation

  1. A number that leaves the same remainder 2 under all three divisors is 2 more than a common multiple of all three.

  2. So find the LCM first: 6=2×36 = 2 \times 3, 8=238 = 2^3, 15=3×515 = 3 \times 5, giving LCM=23×3×5=120\mathrm{LCM} = 2^3 \times 3 \times 5 = 120.

  3. The smallest such number is therefore 120+2=122120 + 2 = 122.

  4. Check: 122=6×20+2=8×15+2=15×8+2122 = 6 \times 20 + 2 = 8 \times 15 + 2 = 15 \times 8 + 2.

Worth noting

The 120 on offer is the LCM itself, which leaves remainder 0, not 2.

Concept
LCM with a common remainder
Typical time
70 s
Your time
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Ten questions from HCF & LCM, at your own pace.

Practise this chapter →

Ten questions from HCF & LCM, at your own pace.