Question

What is a perfect square between 81 and 121

Answer 1

100 is the answer because it is the only number between 81 and 121

Answer 2

Let's set it up to make it easier:

81 = 9
? = ?
121 = 11.

When taking note of perfect squares and their roots, they tend to be written in numeric order (1,2,3...). We know that the number 10 is in between 9 and 11, so we need to find out the square of 10. 
10^2 (or 10*10 )= 100. 100 = 10.