210.25=21025*10^(-2) To find the root of root of 21025, root of 25=5, largest number whose square is less than 210 is 14 So square root is 145 and square root of 10^(-2) is 10^(-1) so answer will be 14.5. Please note this is an approximation method. It will give exact answer if the given number is a perfect square