Question

A work crew had two pumps one new one old the new pump can fill the same tank in 5 hours and the old pump can fill the same tank in 7 hours. How much of a tank can be filled in 1 hour with the new pump ? With the old pump?

Answer 1

• new pump: 1/5 tank
• old pump: 1/7 tank

Explanation:

This gets to the essence of rate problems. The "unit rate" can be inverted to suit the problem at hand.

For the new pump, one way to express its ability to pump is ...

5 hours/tank

Inverting that, we get ...

1/(5 hour/tank) = (1/5) tanks/hour

The pump can fill 1/5 of the tank in 1 hour.

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For the old pump, the same thing works. Inverting the given rate gives ...

1/(7 hours/tank) = (1/7) tanks/hour

The pump can fill 1/7 of the tank in 1 hour.