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
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- Brent@GMATPrepNow
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I'm assuming that the question involves exponents (even though it doesn't appear so)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
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.
- linkinpark
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Hi Brent,
I'm slightly confused here regarding stmt 1, aren't x=3 and y = 2 the only values that satisfy (2^x)(3^y) = 72?
I chose D at first.
thanks
I'm slightly confused here regarding stmt 1, aren't x=3 and y = 2 the only values that satisfy (2^x)(3^y) = 72?
I chose D at first.
thanks
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Thanks guys. Yes, should be exponents. That's what I thought.
linkin-as Brent explained, because the question stem doesn't state INTEGER, there could be multiple answers (Brent provides 2).
wow I haven't logs since high school
linkin-as Brent explained, because the question stem doesn't state INTEGER, there could be multiple answers (Brent provides 2).
wow I haven't logs since high school
- linkinpark
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I'm still not out of confusion, from my knowledge we're not tested on logarithms on GMAT.
can you tell me what other values of x and y satisfy statement 1 apart from x=3 and y = 2
can you tell me what other values of x and y satisfy statement 1 apart from x=3 and y = 2
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linkin-
no, logs are not tested. the point that brent was making is that there are other possibilities since x and y do not have to be INTEGERS. this is actually an important concept that must be understood because it's pretty pervasive throughout the gmat.
orig equation -->(2^x)(3^y) = 72
for example, x could be 1/2, then 2 ^ 1/2, which equals sqrt(2) = 1.4
...then 1.4 * 3 ^ y = 72.
Without going further, you have an equation with one variable so if you wanted to you could solve for y.
no, logs are not tested. the point that brent was making is that there are other possibilities since x and y do not have to be INTEGERS. this is actually an important concept that must be understood because it's pretty pervasive throughout the gmat.
orig equation -->(2^x)(3^y) = 72
for example, x could be 1/2, then 2 ^ 1/2, which equals sqrt(2) = 1.4
...then 1.4 * 3 ^ y = 72.
Without going further, you have an equation with one variable so if you wanted to you could solve for y.
- linkinpark
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for a moment I agree with you on this but wouldn't it be the same case with stmt 2 ?? sorry for dragging the topic but i feel uneasy until I get it downpkw209 wrote:linkin-
no, logs are not tested. the point that brent was making is that there are other possibilities since x and y do not have to be INTEGERS. this is actually an important concept that must be understood because it's pretty pervasive throughout the gmat.
orig equation -->(2^x)(3^y) = 72
for example, x could be 1/2, then 2 ^ 1/2, which equals sqrt(2) = 1.4
...then 1.4 * 3 ^ y = 72.
Without going further, you have an equation with one variable so if you wanted to you could solve for y.
thanks
- linkinpark
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