Pipe A fills one-third of a tank in 4 hours and pipe B fills one-quarter of it in 2 hours. A is opened alone first, and B joins when the tank is half full. How long does the whole filling take?

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Accepted Answer

8.4 h. A takes 12 h, B 8 h. First half by A: 6 h. Then 1/12+1/8=5/24 per hour; half takes 2.4 h. Total 8.4 h. (4.8 h is both from the start.)

Pipe A fills one-third of a tank in 4 hours and pipe B fills one-quarter of it in 2 hours. A is opened alone first, and B joins when the tank is half full. How long does the whole filling take?

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