20. Pump A can fill a tank of water in 4 hours. Pump B can fill the same tank in 6 hours. Both pumps are started at 8:00 a. m. to fill the same empty tank. An hour later, pump B breaks down and took one hour to repair and was restarted again. When will the tank be full? (round your answer to the nearest minute).

Question

Mathematics

Erin Murphy

12 August, 13:14

20. Pump A can fill a tank of water in 4 hours. Pump B can fill the same tank in 6 hours. Both pumps are started at 8:00 a. m. to fill the same empty tank. An hour later, pump B breaks down and took one hour to repair and was restarted again. When will the tank be full? (round your answer to the nearest minute).

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Marguerite · Answer 1

Pump A fills 1/4 of the tank per hour, and pump B fills 1/6 of the tank per hour. Working together, then, they fill 5/12 of the tank in an hour. As a result, after one hour, they fill 5/12 of the tank. After the next hour, 2/3 is filled, because only 1/4 of the tank is filled since Pump B is broken. In the third hour, 1/3 of the tank is left. This takes (1/3) / (5/12), or 4/5, of an hour. This is 48 minutes. Therefore, it takes two hours and 48 minutes to fill the tank, finishing at 10:48.