A gallon of paint covers 20 ft2 of surface area. how many revolutions can an 8 in. wide paint roller with a diameter of 3 in. make before using up a 5-gal can of paint?

We first compute for the surface area of the roller and the total area covered by the 5 gal paint

1gal = 20 ft2

5 gal = 20ft2 x 5

= 100ft2

1 rev = surface area of the side of the cylinder

1 rev = 2pirh

where

radius = 1.5 in=0.125 ft

h = 8 in=0.67 ft

1 rev = 0.53 ft2

5 gal = 100ft2

total revolutions = 100ft2/0.53ft2

total revolutions = 188.68 revoluions

A 5 gal paint can take 188.68 revolutions of paint roller with 8in wide and diameter of 3 in.