Question 1079082
The rate of Perez family water usage = 25 l/h; the rate of Murphy family water usage = 30 l/h
Let P = the amount of time the Perez family sprinkler was on.
Then 40 - P is the amount of time the Murphy's sprinkler was on.
The total amount of water used is:
25*P + 30(40-P) = 1125
Solving for P gives P = 15 hours
Thus the Murphy family used their sprinkler for 25 hours