Question
Pipe A alone can fill 75% of a cistern in 18 minutes.
When both Pipe A and Pipe B are opened together, they can fill the entire cistern in 33 minutes. How long would it take for Pipe B alone to empty the full cistern?Solution
Time taken by pipe 'A' alone to completely fill the cistern = 18 ÷ 0.75 = 24 minutes
So, let the capacity of the cistern = L.C.M of 24 and 33 = 264 units
So, efficiency of pipe of 'A' = 264 ÷ 24 = 11 units/minute
Combined efficiency of pipes 'A' and 'B' = 264 ÷ 33 = 8 units/minute
So, efficiency of pipe 'B' alone = 8 - 11 = 3 units/minute (outlet)
So, time taken by pipe 'B' alone to empty the cistern = 264 ÷ 3 = 88 minutes
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