Question

Estimate square root 250 to two decimal points

Answer 1

15.81 in a calculator it is the tick symbol

Answer 2

OK, the square root of 250 is 15.811 . . . 
but since this can't be expressed as a decimal for your purposes, let's try factoring. Since 250 ends in a zero, only numbers 5 or 0 or those ending in 5 or 0 could be factors. 
The square root of 250 can be factored into the square root of 25 and the square root of 10. 
The square root of 25 is exactly 5, and the exact square root of 10 is another decimal, so your simplified answer can be expressed as 5 times the square root of 10.