Question

The Lewis family and the Martin family each used their sprinklers last summer. The water output rate for the Lewis family's sprinkler was 30L per hour. The water output rate for the Martin family's sprinkler was 15L per hour. The families used their sprinklers for a combined total of 55 hours, resulting in a total water output of 1350L. How long was each sprinkler used

Answer 1

Martin family: 20 hours

Lewis family: 35 hours

Explanation:

Let's say that the Lewis family sprinklers were out for L hours and the Martin family's sprinklers were out for M hours. We know that for each hour that the Lewis family sprinkler was on, 30L of water was put out. We can thus write the Lewis family sprinkler water output as 30L per each hour of L = 30 * L. Similarly, the Martin family sprinkler water output = 15 * M .

We know that the total hours for the sprinklers is 55, so L + M = 55. The total water output for the sprinklers is the sum of the sprinkler outputs, so 30 * L + 15 * M = 1350

L + M = 55

30 * L + 15 * M = 1350

One way to solve this would be to solve for L in the first equation and substitute that into the second

subtract M from both sides in the second equation

55 - M = L

30 * (55-M) + 15 * M = 1350

30 * 55 - 30 * M + 15 * M = 1350

1650 - 15M = 1350

subtract 1650 from both sides to isolate the M and its coefficient

-15M = -300

divide both sides by -15 to isolate M

M = 20

L = 55-20 = 35