Find the least number which must be added to 8400 to obtain a perfect square.

Using the long division method:

The next natural number that is a perfect square can be obtained by squaring the next natural number of the obtained quotient, i.e. 91.

Therefore square of $(91+1)=92^{2}=8464$

Number that should be added to the given number to make it a perfect square $=8464-8400=64$ The perfect square thus obtained is 8464 and its square root is 92 .