Question

The Griffin family and Gray family each used their sprinklers last year . The water output rate for the Griffin family's sprinkler was 30 L per hour. The water output rate for the Grays family's sprinkler was 40 L per hour. The family's used their sprinkler for a combined total of 55 hours resulting in a total water output of 1950 L. How long was each sprinkler used?

Answer 1

x=griffin time
y=gray time

30x+40y=1950
x+y=55

divide first equaion by 10 to simplify stuff
3x+4y=195

multipply second equation by -3 and addd to second

3x+4y=195
-3x-3y=-165 +
0x+1y=30

y=30

x+y=55
x+30=55
mius 30
x=25

griffins's sprinkler: 25 hours
grays's sprinkler: 30 hours