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Re: Good Equation Problem [#permalink]
20 Apr 2010, 07:13

Hussain15 wrote:

If X^3Y = 24, what is the value of X^3Y^3 – X^2Y^2? (1) X^2Y^2 = 36. (2) X^3Y^2 = 72.

1. you can write it as X*X*Y*Y = 36. there are 2 pairs of X*Y so X*Y = +-6 since we dont know if the 6 is positive or negative and the questions has you raise to an odd power A is INSUFF

2. we know from the question X^3 * Y =24 and this choice has an extra Y so the difference is a factor of 3 so Y=3. now plugging back in Y you find X=2 so SUFF.

Re: Good Equation Problem [#permalink]
26 Sep 2010, 00:39

answer is A....explanation:- Statement 1 tells that XY =+6 or -6 but it is given that X2*XY is possitive hence XY has to be positive.....2nd statement tells that X is posstive but you can not derive the value of XY.

Re: Good Equation Problem [#permalink]
26 Sep 2010, 00:44

deeplakshya wrote:

answer is A....explanation:- Statement 1 tells that XY =+6 or -6 but it is given that X2*XY is possitive hence XY has to be positive.....2nd statement tells that X is posstive but you can not derive the value of XY.

Statement 2 says X is positive -----correct

the question says x^3 *y = 24 = positive => only possible when x and y are of same sign =>either -ve or +ve

since x is positive y will also be positive. _________________

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