The people who use sprinklers

Question

The Roberts family and the Coleman family each used their sprinklers last summer. The water output rate for the Roberts family's sprinkler was 20L per hour. The water output rate for the Coleman family's sprinkler was 40L per hour. The families used their sprinklers for a combined total of 75 hours, resulting in a total water output of 2200L. How long was each sprinkler used?

Answer 1

r and c add up to 75, so r = 75-c

20(75-c) + 40c = 2200

1500 - 20c + 40c = 2200

20c = 700

c = 35

Since r+c=75

r = 40 ■