Question

Pipe ‘A’ and pipe ‘B’, together can fill 20% of a tank in 8 hours while pipe ‘C’ takes 50 hours to empty it. Pipe ‘A’ and pipe ‘B’ were opened together. After 25 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 42 hours Correct Answer Incorrect Answer
C 100 hours Correct Answer Incorrect Answer
D 49 hours Correct Answer Incorrect Answer
E 35 hours Correct Answer Incorrect Answer

Solution

Time taken by pipe ‘A’ and pipe ‘B’, together to fill the tank = 8/0.20 = 40 hours
Let the total capacity of tank = 200 units
Efficiency of pipe (A + B) = 200/40 = 5 units/hour
Efficiency of pipe ‘C’ = 200/50 = 4 units/hour
Tank filled by pipe (A + B) in 25 hours = 25 × 5 = 125 units
Time taken by all three pipes to fill the remaining tank = (200 – 125)/(5 – 4) = 75 hrs
Total time taken = 25 + 75 = 100 hours

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