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Question

Pipe ‘A’ and pipe ‘B’, together can fill 20% of a tank in 7 hours while pipe ‘C’ takes 36 hours to empty it. Pipe ‘A’ and pipe ‘B’ were opened together. After 31 hours, pipe ‘C’ is also opened. Find the total time taken to fill the empty tank this way.

A 160 hours Correct Answer Incorrect Answer
B 175 hours Correct Answer Incorrect Answer
C 150 hours Correct Answer Incorrect Answer
D 145 hours Correct Answer Incorrect Answer

Solution

Time taken by pipe ‘A’ and pipe ‘B’, together to fill the tank = 7/0.20 = 35 hours
Let the total capacity of tank = 1260 units
Efficiency of pipe (A + B) = 1260/35 = 36 units/hour
Efficiency of pipe ‘C’ = 1260/36 = 35 units/hour
Tank filled by pipe (A + B) in 31 hours = 31 × 36 = 1116 units
Time taken by all three pipes to fill the remaining tank = (1260 – 1116)/(36 – 35) = 144 hrs
Total time taken = 144 + 31 = 175 hours

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