Find the greatest number of three digits which is a perfect square.

The greatest number with three digits is 999. To find the greatest perfect square with three digits, we must find the smallest number that must be subtracted from 999 in order to get a perfect square. For that, we have to find the square root by the long division method as shown below:
 
So, 38 must be subtracted from 999 to get a perfect square.

999 − 38 = 961

961 = 312

Hence, the greatest perfect square with three digits is 961.