##### Example 1

Ernie can plow a field alone in four hours. It takes Sid five hours to plow the same field alone. If they work together (and each has a plow), how long will it take to plow the field?

First, circle what you must find— *how long …together.* Work problems of this nature may be solved by using the following equation.

Therefore,

Finding a common denominator

Cross multiplying

Therefore, it will take them hours working together.