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ASVAB · Number Properties

Which of the following is a prime number?

Reviewed by Jordan Morley, Editorial Lead at 247SimpleTests. Written by the 247SimpleTests Editorial Team from the official source material cited on every question.

Correct answer

37

  1. A 51
  2. B 21
  3. C 27
  4. D 37

Why this is the answer

37 is prime — only divisible by 1 and 37. 21 = 3×7; 27 = 3×9; 51 = 3×17. A prime has exactly two factors, 1 and itself. To test an odd number, try dividing by the small primes (3, 5, 7) up to its square root: 37 is not divisible by 3 (3 + 7 = 10, not a multiple of 3), does not end in 0 or 5, and 7 × 5 = 35 and 7 × 6 = 42 miss it, so it is prime. The digit-sum test for 3 catches all three distractors quickly: 21 (2 + 1 = 3), 27 (2 + 7 = 9) and 51 (5 + 1 = 6) are all multiples of 3.
Source: ASVAB MK, Prime Numbers

Practice more questions

This question is from our ASVAB Practice Tests practice test. Take the full practice test to test your knowledge across all Number Properties and other topics.

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About this topic: Number Properties

Number properties cover primes and composites, factors and multiples, LCM and GCF, order of operations, divisibility rules, integers and absolute value — the vocabulary and rules the rest of the section assumes. This is one of 7 Mathematics Knowledge questions on number properties, each with a full explanation on a single study page.

New to this exam? Our ASVAB exam guide explains the format, scoring, and how to prepare.

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