Question

The sum of all the prime factors of $m$ is 9. Which of the following is the number $m$.

• A. 15
• B. 28
• C. 20
• D. 63

Answer 1

The correct option is C 20

The prime factors of each number:
15 = 3 $\times$ 5; Sum = 3 + 5 = 8
28 = 2 $\times$ 2 $\times$ 7; Sum = 2 + 2 + 7 = 11
20 = 2 $\times$ 2 $\times$ 5; Sum = 2 + 2 + 5 = 9
63 = 3 $\times$ 3 $\times$ 7; Sum = 3 + 3 + 7 = 13
$\therefore$ $m=20$