I think the answer is 1/6, unless I am missing something. Whats the OA?
We have 4 options. (x+y), (x-y), (5x-y), (x+5y)
Total number of combination we can have = 4C2 = 6 possibilities.
only 1 combination holds true for expression x^2 - (by)^2
i.e. (x+y)(x-y)= x^2 - (1y)^2
1 is also an integer which can be placed instead of b
Therefore the probability is 1/6.
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