Question : Two pipes A and B can fill a cistern in
Option 1: 40
Option 2: 35
Option 3: 30
Option 4: 50
Correct Answer: 35
Solution :
LCM of 12.5 and 25 = 25
Capacity of the cistern = 25 units
Efficiency of A =
Efficiency of B =
Combined efficiency of A and B = 2 + 1 = 3 units/hour
Time taken by A and B to fill the cistern without leakage =
Time taken by A and B to fill the cistern with leakage = 8 hours 20 mins + 1 hour 40 mins = 10 hours
The combined efficiency of A and B with leakage =
Efficiency of leakage = 3 – 2.5 = 0.5 units/hour
Time required by the leak to empty the full cistern =
Time required to empty 70% of the tank =
Hence, the correct answer is 35.
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