Pipes and Cistern
 Pipe A can fill a tank in 45 hrs and pipe B can fill it in 36 hrs. If both the pipes are opened in the empty tank. In how many hours will it be full?

 10 hr
 15 hr
 20 hr
 28 hr

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Part filled by A in 1 hr= (1/45)
Part filled by B in 1 hr= (1/36)Correct Option: C
Part filled A in 1 hr= (1/45)
Part filled B in 1 hr= (1/36)
Part filled by (A+B) together in 1 hr=(1/45)+(1/36)=1/20
So, The tank will be full in 20 hr.
 If a pipe fills a tank in 6 h, then what part of the tank will the pipe fill in 1 h?

 1/3
 1/6
 1/4
 1/5

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We know that, when a pipe fills a tank in m h, then the part of tank filled in 1 h = 1/m
Correct Option: B
We know that, when a pipe fills a tank in m h, then the part of tank filled in 1 h = 1/m
Here, m = 6
∴ Required part of the tank to be filled in 1h = 1/6 part
 A cistern is normally filled in 8 hours but takes two hours longer to fill because of a leak in its bottom. If the cistern is full, the leak will empty it in ?

 16 hrs.
 20 hrs.
 25 hrs.
 40 hrs.

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Work done by leak in 1 hour = (1/8  1/10) = 1/40
Correct Option: D
Work done by leak in 1 hour = (1/8  1/10) = 1/40
∴ The leak will empty the cistern in 40 hours.
 A pipe can empty a tank in 12 minutes and another pipe can empty it in 16 minutes. If both the pipes are opened simultaneously, find the time in which a full tank is emptied ?

 6 minutes
 6^{1}/_{7} minutes
 6^{2}/_{7} minutes
 None of these

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Required answer = (12 x 16) /(12 + 16) = 48 / 7 = 6^{6}/_{7} minutes.
Correct Option: D
Required answer = (12 x 16) /(12 + 16) = 48 / 7 = 6^{6}/_{7} minutes.
 A cistern is normally filled in 8 hrs. but takes 2 hrs. longer to fill because of a leak in its bottom. If the cistern is full, the leak will empty it in ?

 16 hrs.
 40 hrs.
 25 hrs.
 20 hrs.

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Here x = 8 hrs. and y = 8 + 2 = 10 hrs.
Now, applying the given rule, we have the
Required answer = (8 x 10) /(10  8) = 40 hrs.Correct Option: B
Here x = 8 hrs. and y = 8 + 2 = 10 hrs.
Now, applying the given rule, we have the
Required answer = (8 x 10) /(10  8) = 40 hrs.