What is the estimated value of the length of a square with an area of 200 square inches?

area of a square is S^2

 so to estimate think of a number when multiplied by itself would equal 200

 think about 10, 10 x 10 = 100 too low

20 x 20 = 400, too high

 so 15 x 15 = 225, pretty close

so try 14, 14 x 14 = 196

 so the actual value is a little over 14

 so 14 would be the right estimate