The Harris family and the Robinson family each used their sprinklers last summer. The water output rate for the Harris family's sprinkler was 40L per hour. The water output rate for the Robinson family's sprinkler was 20L per hour. The families used their sprinklers for a combined total of 65 hours, resulting in a total water output of 1800L . How long was each sprinkler used?

Question

anonymous · Answer

We should be able to come up with 2 equations.
Let x = hours the 40L sprinkler ran
Let y = hours the 20L sprinkler ran

Obviously, X + Y = 65....there's one equation.

Also note the
Water output of 40L sprinkler + Water output of 20 L sprinkler = 1800L
                40x                      +                 60y                       = 1800

There's your 2nd equation