If Pipe A can fill a tank in 80 minutes and Pipe B has a diameter that is 3 times larger than Pipe A, how long will it take for both pipes to fill the tank together when it is empty?

Answer Choices

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6 minutes

7 minutes

8 minutes

Correct

10 minutes

12 minutes

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Official Explanation

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Pipe A can fill a tank in 80 minutes. Pipe B, with a diameter 3 times that of Pipe A, will fill the tank faster. The volume filled by Pipe B is 3^2 times that of Pipe A, which means it fills the tank in 80/9 = 8.89 minutes. The…

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What this question tests

What it tests

Your ability to combine individual work rates, usually by working with the fraction of a job completed per unit of time.

Common trap

Adding the times instead of the rates, or forgetting to take the reciprocal when combining rates.