Question

Which is a perfect square? 72 81 90 99

Answer 1

81 is perfect square.

Explanation:

Given numbers 72 81 90 99 .

We have to choose the number out of given options that are perfect squares.

PERFECT SQUARES are those numbers that be written as product of two equal numbers. Also perfect squares are those numbers that can be written as square of a number.

Thus, for given numbers

1) 72 = 8 × 9

2) 81= 9 × 9

3) 90= 9 × 10

4) 99 = 9 × 11

Thus, out of given option only 81 is written as product of two equal numbers.Thus 81 is perfect square.

Answer 2

Your perfect square would be 81, which is the square of 9. When encountering these type of questions in the future, if you don't have the squares memorized, you may just have to go through all of them through guessing and checking by squaring numbers starting from 2.