Question

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

• A. 15
• B. 28
• C. 20
• D. 63

Answer 1

The correct option is C

20

The prime factors of each of the given options are as follows:

15 = 3 $\times$ 5 $\Rightarrow$ sum of its prime factors = 3 + 5 = 8

28 = 2 $\times$ 2 $\times$ 7 $\Rightarrow$ sum of its prime factors = 2 + 2 + 7 = 11

20 = 2 $\times$ 2 $\times$ 5 $\Rightarrow$ sum of its prime factors = 2 + 2 + 5 = 9

63 = 3 $\times$ 3 $\times$ 7 $\Rightarrow$ sum of its prime factors = 3 + 3 + 7 = 13

Only the number 20 satisfies the given condition.

$\therefore$ $m=20$