How long was each sprinkler used?

Question

The Clark family and the Griffin family each used their sprinklers last summer. The water output rate for the Clark family's sprinkler was 25 L per hour. The water output rate for the Griffin family's sprinkler was 40 L per hour. The families used their sprinklers for a combined total of 75 hours , resulting in a total water output of 2475 L. How long was each sprinkler used?

Answer 1

NOTE: Units are VERY IMPORTANT:

(Liters/hour) * hours = Liters

( 25 L/hr) * ( t hr ) + ( 40 L/hr) * ( 75 - t ) hr = 2475 L

25 t L + 3000 L - 40 t L = 2475 L

1. 15 L = - 525 L

t = 35 hr for Clarks

75-t = 40 hr for Griffins

CHECK (always good):

Does 25 * 35 + 40 * 40 = 2475 ?

2475 = 2475 ? YES

Answer 2