The possible perfect squares <100 are : 1,4,9,16,25,36,49,64,81
5 of them are odd, and 4 of them are even.
if x+y and x-y are equal to two perfect squares, then the two perfect squares must be either even or odd.
for example, if we assume that x+y = 9 (odd) and x-y = 1 (odd), then x = 5 and y = 4
but if we assume that x+y = 16 (even) and x-y = 1 (odd), there will be no valid integer values.
the number of valid pairs for the odd perfect squares = 5C2 = 10
the number of valid pairs for the even perfect squares = 4C2 = 6
total = 16
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