Textbook 79, Question 19

A square picture with an area of 100cm² is mounted on a square piece of matting. The matting has 2.5 times the area of the picture. If the picture is centered on the matting, what width of matting is visible around the outside of the picture. Give your answer to the nearest tenth of a centimeter.

So we know that the picture in the middle is 100cm²

So I if we find out what 100cm² x 2.5 is we get 250. Now we need to find the square root of 250 which we get 15.8cm.

 The space between the 10cm and 15.8cm line is 5.8cm
if we move the square in the middle to the very center, that is like splitting that space in half, so 5.8÷2 you get 2.9cm