SAT Math Question of the Day

Math Category: Prime Number Factors:

Q: What are the prime factors of 20?

  1. 5
  2. 2 and 5
  3. 1, 2, and 5
  4. 2, 4, 5, 10
  5. 1, 2, 4, 5, 10, and 20

UNANSWERED.

The correct answer is B.

A: 2 and 5. The factors of 20 are 1, 2, 4, 5, 10, and 20. But this question asked for the "prime factors"; that is which factors of 20 are also prime numbers. So that eliminates 1, because 1 is not a prime by definition. Also eliminated are 4, 10, and 20 because they are each divisible by three or more factors and thus not a prime. That leaves 2 and 5.