GMATinsight wrote:

How many factors of 3600 are odd?

A) 3

B) 6

C) 9

D) 18

E) 45

Source:

http://www.GMATisnight.comSince most of the answer choices are pretty small, it might not take long to LIST all of the odd factors.

We'll use the fact that 3600 = (2)(2)(2)(2)(3)(3)(5)(5) AND the fact that ODD x ODD = ODD

So, we'll work solely with the ODD primes: (3)(3)(5)(5)

So, the ODD factors of 3600 are:

- 1

- 3

- 5

- (3)(3)

[we need not evaluate this, since we'll just going to count the factors in our list]- (3)(5)

- (5)(5)

- (3)(3)(5)

- (3)(5)(5)

- (3)(3)(5)(5)

Done!

Answer:

Cheers,

Brent

_________________

Brent Hanneson – GMATPrepNow.com

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