If x and y are distinct positive integers, what is the value of x^4 - y^4?
(y^2 + x^2)(y + x)(x - y) = 240
x^y = y^x and x > y
[spoiler]Source: Platinum GMAT OA:D[/spoiler]
Not satisfied with the explanation posted there. I doubt if it is a good level qn.
PS: Post edited to correct the typo.
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anantbhatia
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Last edited by anantbhatia on Fri Oct 08, 2010 12:41 am, edited 1 time in total.
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Ian Stewart
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Statement 1 is sufficient; if you expand the left side, you get x^4 - y^4.anantbhatia wrote:If x and y are distinct positive integers, what is the value of x^4 - y^4?
(y2 + x2)(y + x)(x - y) = 240
xy = yx and x > y
[spoiler]Source: Platinum GMAT OA:D[/spoiler]
Not satisfied with the explanation posted there. I doubt if it is a good level qn.
Statement 2 is clearly not sufficient. Of course xy = yx; that's always true, so that isn't useful information. We already know that x and y aren't equal, so x > y only tells us that x^4 - y^4 is positive. It might be that y = 1 and x = 2, or that y = 1 and x = 3, and the value of x^4 - y^4 will be different in each case. So the answer is A unless Statement 2 has been miscopied.
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anantbhatia
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Sorry Ian,
Reposting:-
If x and y are distinct positive integers, what is the value of x^4 - y^4?
(y^2 + x^2)(y + x)(x - y) = 240
x^y = y^x and x > y
Reposting:-
If x and y are distinct positive integers, what is the value of x^4 - y^4?
(y^2 + x^2)(y + x)(x - y) = 240
x^y = y^x and x > y
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deepak123gmat
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2) x^y = y^x and x > y
is true only for x = 4 and y=2.
If you keep on increasing values of x and y. then y^x becomes bigger than x^y.
Just input these values in x^4 - y^4 and you will get 240.
is true only for x = 4 and y=2.
If you keep on increasing values of x and y. then y^x becomes bigger than x^y.
Just input these values in x^4 - y^4 and you will get 240.
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anantbhatia
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Hi all,
The basic question is:-
Using (2), is it possible to get the required result? Or is it only possible to get the result only by plugging in the values. Also, if it is the latter case, is that acceptable?
The basic question is:-
Using (2), is it possible to get the required result? Or is it only possible to get the result only by plugging in the values. Also, if it is the latter case, is that acceptable?
