A toy company makes rubber balls with a diameter of 20cm. How much rubber would be saved per ball if the balls had a diameter of 15cm?
diameter of 20 = radius of 10
diameter of 15 = radius of 7.5
To find the savings.......take the difference in surface areas =
4pi ( 10^2 - 7.5^2) =
4pi ( 100 - 56.25) =
4 pi * 43.75 cm^2 =
175 pi cm^2
