SOLUTION: The Wong family and the Kelly family each used their sprinklers last summer. The water output rate for the Wong family's sprinkler was 35L per hour. The water output rate for

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Question 1066003: The Wong family and the Kelly family each used their sprinklers last summer. The water output rate for the Wong family's sprinkler was
35L
per hour. The water output rate for the Kelly family's sprinkler was
20L
per hour. The families used their sprinklers for a combined total of
35
hours, resulting in a total water output of
925L
. How long was each sprinkler used?
Answer by josgarithmetic(39628) About Me  (Show Source):
You can put this solution on YOUR website!
This is a constant rates problem exercise. 

                       RATE       TIME(hours       VOLUME(liters)
WONG                    35          w                35w
KELLY                   20          k                20k
TOTAL                               35                925


system%28w%2Bk=35%2C35w%2B20k=925%29

The volume sum equation simplified,
7w%2B4k=185
-
From the time sum, k=35-w. Substitute this.
7w%2B4%2835-w%29=185
7w%2B4%2A35-4w=185
3w=185-4%2A35
3w=45
highlight%28w=15%29------------Hours for the Wong's.

highlight%28k=20%29----------hours for the Kelly's.