Question

Which of the following will have 9 in it's unit place?

• A. ${42}^2$
• B. ${23}^2$
• C. ${58}^2$
• D. ${16}^2$

Answer 1

The correct option is B ${23}^2$

The digit in unit's place for the square of a number is defined by the digit in the unit's place of the original number.

Original number's unit place	Squared number's unit place
0	0
1	1
2	4
3	9
4	6
5	5
6	6
7	9
8	4
9	1

For natural numbers having 3 or 7 in its unit place, their squares have 9 in their unit place.

From the options, only 23 has 3 in the unit's place.
${23}^2=529$