Question

The Chen family and the Aoki family each used their sprinklers last summer. The water output rate for the Chen family's sprinkler was 40L per hour. The water output rate for the Aoki family's sprinkler was 25L per hour. The families used their sprinklers for a combined total of 65 hours, resulting in a total water output of 2000L. How long was each sprinkler used?

Answer 1

Chen family used the sprinklers for 25 hours

Aoki family used the sprinklers for 40 hours

Explanation:

Let C be the number of hours the Chen family used the sprinklers and let A be the number of hours the Aoki family used the sprinklers

Total hours used

=> C + A = 65 (1)

Total water usage for Chen family = 40C (40 L per hour x no. hour)
Total water usage for Aoki family = 25C (25 L per hour x no. hours)

Total used by both families = 2000 L

So
40C + 25A = 2000 (2)

Therefore we have two equations in 2 variables which can be solved simultaneously

Multiply (1) by 25:
==> 25C + 25A = 25 x 65
==> 25C + 25A = 1,625 (3)

Subtract (3) from (2) to eliminate the A term:
(2) - (3) ==>
40C + 25A - (25C + 25A ) = 2000 - 1625

40C + 25A - 25C - 25A = 375
40C - 25C = 375
15C = 375
C = 375/15

C = 25
So the Chen family used the sprinklers for 25 hours

Since C + A = 65
A = 65 - C
==> A = 65 - 25
A = 40
The Aoki family used the sprinklers for 40 hours