Inlets A and B fill a tank in 20 and 24 minutes, and outlet C empties it in 30 minutes. All three are opened on the empty tank; after 6 minutes C is closed, and 4 minutes after that A is closed too. How much longer does B need to fill the tank?

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Accepted Answer

6.8 min. First 6 min: 6 (6+5-4/120 )=42/120. Next 4 min (A, B): 4×11/120=44/120. Filled 86/120; left 34/120. B: 34/120×24=6.8 min.

Inlets A and B fill a tank in 20 and 24 minutes, and outlet C empties it in 30 minutes. All three are opened on the empty tank; after 6 minutes C is closed, and 4 minutes after that A is closed too. How much longer does B need to fill the tank?

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