Multiple choice

The rates of water flow through three pipes A, B and C are in the ratio 4 : 9 : 36. An empty tank can be filled up completely by pipe A in 15 hours. If all the three pipes are used simultaneously to fill up this empty tank, the time, in minutes, required to fill up the entire tank completely is nearest to

  1. 73

  2. 78

  3. 76

  4. 71
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Pipe A fills in 15 hours. Ratio A:B:C = 4:9:36. If A=4 units/hr, B=9, C=36. Total capacity = 4 * 15 = 60 units. Combined rate = 4+9+36 = 49 units/hr. Time = 60/49 hours = (60/49) * 60 minutes = 3600/49 = 73.46 minutes. Nearest is 73.

AI explanation

Since pipe A fills the tank in 15 hours and the rates of pipes A, B, and C are in the ratio 4:9:36, pipe B fills it in 15 times 4/9 hours and pipe C takes 15 times 4/36 hours. This gives individual times of 20/3 hours for B and 5/3 hours for C. The combined hourly rate is 1/15 + 3/20 + 3/5, which equals 49/60 of the tank per hour. The total time required is the reciprocal of this rate, 60/49 hours, which is roughly 1.22 hours or about 73 minutes. The result is 73 minutes.

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