SOLUTION: A large pump can fill a tank in 28 minutes. Both a large pump and a small pump can fill a tank in 20 minutes. How long would it take the small pump to fill the tank by itself?

Question 1040135: A large pump can fill a tank in 28 minutes. Both a large pump and a small pump can fill a tank in 20 minutes. How long would it take the small pump to fill the tank by itself?
Found 2 solutions by addingup, ikleyn:
Answer by addingup(3677)   (Show Source): You can put this solution on YOUR website!
(28*x)/(x+28) = 20
28*x = 20(x+28)
28x = 20x+560
Subtract 20x from both sides:
8x = 560
x = 70 minutes
Answer by ikleyn(52800)   (Show Source): You can put this solution on YOUR website!
.
A large pump can fill a tank in 28 minutes. Both a large pump and a small pump can fill a tank in 20 minutes.
How long would it take the small pump to fill the tank by itself?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Two pumps working together fill of the tank volume per minute.

One pump (large) fills of the tank volume per minute.

Hence, the second pump fills = = = = of the tank volume per minute.

It means that it will take 70 minutes for the second pump to fill the tank working alone.

      Lesson to learn from this solution: use rates of work.
      You can add and distract them. It does make sense.

For many other joint-of-work problems see the lessons
    - Using Fractions to solve word problems on joint work
    - Solving more complicated word problems on joint work
    - Selected joint-work word problems from the archive
in this site.

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