Question

Question #efd44

Answer 1

(D) `30`

Explanation:

Here's a good rule for this problem: All the factors for a number (except 1) must be able to be produced by a combination of products of the prime factors.

That might sound confusing. Let me give you an example. The prime factors for 42 are 2, 3, 7. The factors of 42 are 1, 2, 3, 6, 7, 14, 21, 42

`2=2`

`3=3`

`6=2*3`

`7=7`

`14=2*7`

`21=3*7`

`42=2*3*7`

See how I was able to form all the factors of 42 (except 1) by only multiplying the prime factors?

Using this rule, we just need to find the choice that has the number that can't be obtained by multiplying the prime factors:

(A) `10=2*5`
(B) `20=2*2*5`
(C) `25=5*5`
(E) `34=17*2`

Therefore, the answer must be (D) 30. Hope this helps!