A fire-station reservoir has two inlets: one fills it in 30 minutes, the other in 70 minutes. If both inlets are opened on the empty reservoir, after how many minutes will it be full?

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Accepted Answer

21. Combined rate = 1/30 + 1/70 = (7 + 3)/210 = 1/21 of the reservoir per minute, so it is full in 21 minutes.

A fire-station reservoir has two inlets: one fills it in 30 minutes, the other in 70 minutes. If both inlets are opened on the empty reservoir, after how many minutes will it be full?

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