Question

find the least and greatest number of 4 digit which are perfect square

Answer 1

This is answer which you want that The square root of greatest digit of four

Answer 2

9999 is largest 4 digit number, and 100^2 is 10000, or 1 greater than the largest 4 digit number. This means that the closest square root of the largest perfect square is most likely 99. So 99^2 (9801)is the largest perfect square of four digits. Here we need largest 4 digit number which is a perfect square.