Question

A box has the shape of a rectangular prism with height 31 cm. If the height is increased by 0.9 cm, by how much does the surface area of the box increase? 31 cm 12 cm 7.2 cm Use pencil and paper. Show your work. Then show a second way to solve the problem. Explain which way you like better and why. The surface area increases by cm2​

Answer 1

First size: SA1 = 2B + Ph, where B = area of the base of the figure, P = perimeter of the base and h = height

SA1 = 2(12*7,2) + (12+7,2)*31 = 172.8 + 595.2 = 768 cm^2

Second size: SA2 = 2B + ph2 (where h2 is the new height, 31.9 cm)
SA2 = 2(12*7,2) + (12+7,2)*31.9 = 785.28 cm^2

It increases (by rounding it down) by 17 cm^2.