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Counting and Basic Probability · Question 13 of 65

Question 13

MediumOriginal question

How many positive whole numbers divide 360 exactly (including 1 and 360)?

Options for question 13

Show the answer and explanation
CorrectNot quiteAnswer D

Correct answer: D

Explanation

  1. Prime factorisation: 360=23×32×5360 = 2^3 \times 3^2 \times 5.

  2. A divisor takes the power of 2 from 0 to 3 (4 ways), of 3 from 0 to 2 (3 ways), of 5 from 0 to 1 (2 ways).

  3. Divisors =4×3×2=24= 4 \times 3 \times 2 = 24.

Worth noting

6 multiplies the exponents 3×2×13 \times 2 \times 1, forgetting that each power can also be 0. 9 adds the choices instead of multiplying. 22 leaves out 1 and 360.

Concept
Counting divisors with the multiplication rule
Typical time
70 s
Your time
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The rule this testsThe counting principle
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Ten questions from Counting and Basic Probability, at your own pace.

Practise this chapter →

Ten questions from Counting and Basic Probability, at your own pace.