Exercises 1-4: Measuring the thickness of a very thin layer of material can be difficult to do directly. For example, with a ruler it would be difficult to measure the thickness of an oil film on water or a coat of paint. 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 1 inch. Use this formula in the following exercises.

A lake covers 2.5 x 10⁷ square feet and contains 7.5 x 10⁸ cubic feet of water. Find the average depth of the lake.

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Thickness= Volume Area