SOLUTION: An 8 hp pump can fill a tank in 8 hours. A smaller 3 hp pump fills the same tank in 12 hours. The pumps are used together to begin filling this tank. After four hours, the 8 hp pum

Question 263393: An 8 hp pump can fill a tank in 8 hours. A smaller 3 hp pump fills the same tank in 12 hours. The pumps are used together to begin filling this tank. After four hours, the 8 hp pump breaks down. How long will it take the smaller pump to fill the tank?
Answer by drk(1908) (Show Source): You can put this solution on YOUR website!
This is a working together problem.
The rate of the 8 hp pump = 1/8
the rate of the 3 hp pump is 1/12
The time together will be 4 hours.
The time that the 3 hp pump works alone is x hrs.
We want to fill only 1 tank
-----
we use the formula

we get

adding the fractions, we get

subtract 5/6 to get

multiply by 12 to get

So, the 3 hp pump must work and additional 2 hours.
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