Saturday 10 January 2015

Filling a Cistern



Pipe S can fill cistern is 2 hours and pipe k can fill a cistern in 3 hours, Pipe Y can empty it in 5 hours. Supposing all the pipes are turned on when the cistern is completely empty, how long will it take to fill?

Answer: 

 1 11/19 Hours. In one hour S fills ½ K fills 1/3 and Y empties 1/5 of the cistern.
With all the pipes working (1/2 + 1/3 – 1/5)
Or 19/30 of the cistern is filled in one hour.
With all the pipes working (30 – 30)
Of the cistern is filled in (30/19) hours.

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