Hi Danielle,

I am going to look at the same question but with the number 43.

The square root of 43 between what two numbers?

I'm going to try some squares.

5² = 25 which is smaller than 43.
6² = 36 which is still smaller than 43.
7² = 49 which is larger than 43.

Thus 43 is between 6² and 7² and hence the square root of 43 is between 6 and 7.

Now you try 21,
Penny