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GMATPrep 2 question

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GMATPrep 2 question

by bkobilov » Thu Sep 30, 2010 8:26 am
Please help.

If two of the four expressions x+y, x+5y, x-y, 5x-y are chosen at random, what is the probability that their product will be of the form of x^2- (by)^2, where b is an integer?

1/2
1/3
1/4
1/5
1/6
OA: E
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by narik11 » Thu Sep 30, 2010 8:32 am
bkobilov wrote:Please help.

If two of the four expressions x+y, x+5y, x-y, 5x-y are chosen at random, what is the probability that their product will be of the form of x^2- (by)^2, where b is an integer?

1/2
1/3
1/4
1/5
1/6
OA: E
Only x+y and x-y can be of the form x^2- (by)^2 from the above given expressions:
And the total possibilities is 6

so its 1/6
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