Question

Which of the following would end with the digit 1?

• A. 123²
• B. 161²
• C. 82²
• D. 77²

Answer 1

The correct option is B

161²

In order to find the unit digit in the square of any number, we need to find the square of the unit digit of the number. The unit's digit of this square will give us the required result. Thus, unit's place of the square of a number with unit digit 1 is also 1.
For example, the unit's place of the square of 64 $[{64}^2=4096]$, which is 6, is same as the unit's place of the square of 4 which is in unit's place of 64.
Hence, ${161}^2$ will have 1 at its units place as $1^2$, which is unit digit of the number, is 1.