Question

If the digit at unit place of a square number is 1, then it is a square of a number___.

• A. whose unit place digit is either 9 or 1.
• B. whose unit place digit is 7.
• C. whose unit place digit is 8.
• D. whose unit place digit is either 5 or 1.

Answer 1

The correct option is A

whose unit place digit is either 9 or 1.

The square of a number 9 = 9 $\times$ 9 = 81

The square of 19 = 19 $\times$ 19 = 361

The square of 29 = 29 $\times$ 29 = 841

The square of 21 = 21 $\times$ 21 = 441

Therefore the unit place digit of a square root has to be either 9 or 1.