CAT Practice : Pipes cisterns, Work time

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Classic Work - Time Question!!

Fetching Water

    Q.20: Bibhor takes 3 hours to fetch as much water as Ahmed can fetch in 2 hours. Deepak takes 5 hours to fetch as much water as Bibhor can fetch in 4 hours. A tank takes 20 hours to fill if all work together. What time would Bibhor take to fill the tank alone?
    1. 50 h
    2. 56 h
    3. 77 h
    4. 66 h


  • Correct Answer
    Choice D. 66 h

Detailed Solution

Let the work done by Ahmed be 60 (LCM of 2,3,4,5)

So, work done per hour by:

Ahmed – = 30
Bibhor – = 20

Bibhor in 4 hours – 20 x 4 = 80

Deepak – = 16

Therefore, total work done in an hour = 30 + 20 + 16 = 66

If all 3 work for 20 hours, total work done = 66 x 20

If Bibhor alone has to work, time taken to do 66 x 20 of work = (work done by Bibhor in 1 hour) = 66 hour

Correct Answer: 66 h

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Mathematicians are creatures of habit. This topic has been called Pipes and Cisterns because someone named it like it long ago. Pipes and Tanks would be much better - at least makes it sound like wartime.