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Question

Pipe ‘A’ and pipe ‘B’, together can fill 20% of a tank in 7 hours while pipe ‘C’ takes 40 hours to empty it. Pipe ‘A’ and pipe ‘B’ were opened together. After 34 hours, pipe ‘C’ is also opened. Find the total time taken to fill the empty tank this way.

A 30 hours Correct Answer Incorrect Answer
B 42hours Correct Answer Incorrect Answer
C 40 hours Correct Answer Incorrect Answer
D 49 hours Correct Answer Incorrect Answer
E 15 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 = 280 units
Efficiency of pipe (A + B) = 280/35 = 8 units/hour
Efficiency of pipe ‘C’ = 280/40 = 7 units/hour
Tank filled by pipe (A + B) in 34 hours = 34 × 8 = 272 units
Time taken by all three pipes to fill the remaining tank = (280 – 272)/(8 – 7) = 8 hrs
Total time taken = 34 + 8 = 42 hours

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