Multiple choice

x and y are integers. x has 3 prime factors (excludes x itself) and y has 4 prime factors (excludes y itself). If the greatest common factor of x and y is 21, how many prime factors does x*y have?

  1. 2

  2. 5

  3. 21

  4. 4
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

21 is the greatest common factor of x and y. So 3 and 7 are two common 2 prime factors of x and y. Hence, x still has one prime factor a and y still has two prime factors b and c. The prime factors of x*y should be a, b, c, 3 and 7, the total number is 5.

Keep practicing — related questions