Question : When operated separately, pipe A takes 5 hours less than pipe B to fill a cistern, and when both pipes are operated together, the cistern gets filled in 6 hours. In how much time (in hours) will pipe B fill the cistern, if operated separately?
Option 1: 15
Option 2: 18
Option 3: 10
Option 4: 9
Correct Answer: 15
Solution :
Let the time it takes for pipe B to fill the cistern when operated separately as
Then, the time it takes for pipe A to fill the cistern when operated separately is
The rates of pipes A and B are
When both pipes are operated together, their rates add up, and the cistern gets filled in 6 hours.
So,
Multiplying through by
Since pipe A takes 5 hours less than pipe B to fill the cistern, then
So, pipe B will fill the cistern in 15 hours.
Hence, the correct answer is 15.
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