Interesting squares problem

[himanshubari]

what is the value of m^4 - n^4
1] m^2 - n^2 = 16
2] m+n = 8

Now the answer is supposed to be C.
But I thought should have been A... is it true that if they would have added the constraint that m and n are integers then the answer would have been A????
as in that case 1] would be sufficient to prove that m = 5 and n = 3 as 5^2 - 3^2 = 16

[keanuxie]

Yes, if M and N are both positive intergers, the answer shall be A.

[esledge]

Right, it sounds like you made the classic DS assumption error: assuming the numbers are integers, because that would be convenient. Sometimes this simply results from plugging test numbers (which are integers for most people...) and forgetting that other test numbers would work.

Actually, I think the answer would be A if m and n were only constrained to be integers--you wouldn't need the constraint that they are positive.

(1) would allow m = +/-5 and n = +/- 3, and m^4 - n^4 would be 625 - 81 = 544 no matter the sign of m and n.