Multiple choice

Pipes P and Q can fill a tank in 10 and 12 hours respectively and C can empty it in 6 hours. If all three are opened at 7 a.m. at what time will one-fourth of the tank be filled?

  1. 10 a.m.

  2. 10 p.m.

  3. 11 p.m.

  4. 11 a.m.
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Combined rate when all three pipes work: 1/10 + 1/12 - 1/6 = (6 + 5 - 10)/60 = 1/60 tank per hour (negative because C empties). To fill 1/4 tank: time = (1/4) / (1/60) = 15 hours. Starting at 7 a.m. + 15 hours = 10 p.m.

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