Measuring the thickness of a very thin layer of material can be difficult to do directly....

Measuring the thickness of a very thin layer of material can be difficult to do directly. For example, it would be difficult to measure the thickness of an oil film on water or a coat of paint with a ruler. However, it can be done indirectly using the following formula.

That is, the thickness of a thin layer equals the volume of the substance divided by the area that it covers. For example, if a volume of 1 cubic inch of paint is spread over an area of 100 square inches, then the thickness of the paint equals inch. Use this formula in the following exercises.

Thickness of Cement A 100-foot-long sidewalk is 5 feet wide. If 125 cubic feet of cement are evenly poured to form the sidewalk, find the thickness of the sidewalk.