Question

least number which must be subtracted from 2581 to make it a perfect square

Answer 1

81 must be sustracted. That makes it 2500 which is a square of 50

Answer 2

By taking The square root of 2581.
We get,
√2581=50.8035....

now 50²=2500
and 51²=2601.

Here 2601 is more near to 2581...

But The question Clearly say's Which No must Be SUBSTRACTED from 2581 to obtain a Perfect square.

And so the Answer is 2581-2500=81.
81 Substracted From 2581 will Give 2500 which is A perfect square [50²]

Hope it Helps...
Regards,
Leukonov.