Give reason to show that none of the numbers 640, 81000 and 3600000 is a perfect square.

According to the property of square numbers, if a number ends with n zeroes, its square ends with 2n zeroes.

2n will always be an even number. The numbers 640, 81000 and 3600000 have 1, 3 and 5 zeroes respectively.

Hence, the numbers 640, 81000 and 3600000 are not a perfect square.