Multiple choice

Three pipes A,B and C alone can fill a tank in 10, 12 and 15 minutes. Then in how much time the tank will be filled if all pipes are opened together?

  1. 6 minutes

  2. 4 minutes

  3. 5 minutes

  4. 7 minutes
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Pipe A fills 1/10 of tank per minute, B fills 1/12, C fills 1/15. Combined rate = 1/10 + 1/12 + 1/15 = 6/60 + 5/60 + 4/60 = 15/60 = 1/4 tank per minute. Time to fill = 1 / (1/4) = 4 minutes. When pipes work together, add their individual rates to get the combined rate, then take the reciprocal.

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