Question

A machine coats metal spheres with a plastic coating. The metal spheres have a radius of 9 mm. The spheres formed by the metal and plastic coating have a radius of 12 mm.
How much plastic coating is on each sphere?
Use 3.14 to approximate pi and express your final answer in hundredths.

Answer 1

Find the volumes of the two spheres and subtract.

V = 4/3 * pi * r^3

V = 4/3 * 3.14 * 9^3

Simplify exponent:

V = 4/3 * 3.14 * 729

Multiply:

V = 3052.08

V = 4/3 * pi * r^3

V = 4/3 * 3.14 * 12^3

Simplify exponent:

V = 4/3 * 3.14 * 1728

Multiply:

V = 7234.56

Subtract the two volumes:

7234.56 - 3052.08 = 4182.48