Two pipes can fill a tank in 12 minutes and 18 minutes. Both are opened together, and the faster pipe is shut after 4 minutes. In how many minutes in all is the tank filled?

Question

Accepted Answer

12. In 4 minutes both fill 4 × (1/12 + 1/18) = 4 × 5/36 = 5/9. The rest, 4/9, takes the slower pipe 4/9 × 18 = 8 min. Total = 4 + 8 = 12 min.

Two pipes can fill a tank in 12 minutes and 18 minutes. Both are opened together, and the faster pipe is shut after 4 minutes. In how many minutes in all is the tank filled?

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