The Kelly family and the Garcia family each used their sprinklers last summer. The water output rate for the Kelly family's sprinkler was 35L per hour. The water output rate for the Garcia family's sprinkler was 20L per hour. The families used their sprinklers for a combined total of 45 hours, resulting in a total water output of 1350L. How long was each sprinkler used?

30 hours

15 hours.

Explanation:

Let the Kelly used sprinkler for t hours and Gracia used the sprinkler for the rest ie (45 - t) hours.

Water output by Kelly = (35 x t) L

Water output by Gracia = 20 (45 - t) L

Total output = 35t + 20 (45 - t)

So, 35 t + 20 (45 - t) = 1350

35 t + 900 - 20 t = 1350

15 t = 450

t = 30 hours

So Kelly used sprinkler for 30 hours and Gracia used it for 45 - 30 = 15 hours.