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Question

Two pipes can fill a cistern in 12 and 20 hours respectively. The pipes are opened simultaneously and it is found that due to leakage in the bottom, 30 minutes extra are taken for the cistern to be filled up. If the cistern is full, what time would the leak take to empty it?

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Solution

The correct option is **A** 120 hours

Cistern filled by both pipes in one hour =112+120=215

Therefore both pipes filled the cistern in 152 hrs.

Now, due to leakage, both pipes filled the cistern in 152+3060=8 hrs.

Therefore due to leakage, part filled in one hour =18

Therefore part of cistern emptied, due to leakage in one hour =215−18=1120

Hence, in 120 hours, the leak would empty the cistern.

Cistern filled by both pipes in one hour =112+120=215

Therefore both pipes filled the cistern in 152 hrs.

Now, due to leakage, both pipes filled the cistern in 152+3060=8 hrs.

Therefore due to leakage, part filled in one hour =18

Therefore part of cistern emptied, due to leakage in one hour =215−18=1120

Hence, in 120 hours, the leak would empty the cistern.

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