ronny13 wrote:
If two of the four expressions x+y, x+5y, x-y, and 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?
A. 1/2
B. 1/3
C. 1/4
D. 1/5
E. 1/6
Only (x+y)(x-y) or one combination satisfies the condition. There are 4!/(2!)*(2!) total possibilities, since two equations are selected and the other two are not selected (YYNN as an anagram).
The odds are 1/6.
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