pkw209 wrote:Hey all,

I think the answer should be B rather than D since the question stem doesn't state positive INTEGER. A brief explanation would be very much appreciated. Thanks!

78) x and y are positive, what is x + y?

a. 2x3y = 72
b. 2x2y = 32

I'm assuming that the question involves exponents (even though it doesn't appear so)
If the question is:
x and y are positive, what is x + y?
(1) (2^x)(3^y) = 72
(2) (2^x)(2^y) = 32
then you're right. The answer should be B.

(1) (2^x)(3^y) = 72
Without getting too out of scope, statement (1) can give us more than one set of values for x and y such that the sum of x and y differ.
Here are two sets:
a) x=3 and y=2 --> x+y equals 5
b) x=log(base2)9 and y=log(base3)8 --> x+y does not equal 5
Don't worry about the logs; they aren't required for the GMAT
INSUFFICIENT


(2) (2^x)(2^y) = 32
(2^x)(2^y) = 2^5
2^(x+y) = 2^5
x+y=5
SUFFICIENT

If the question had restricted x and y to positive integers, the answer would have been D.