[6 minutes] Two pipes can fill a tank in 12 minutes and 20 minutes respectively. Both pipes are opened together

For Competitive Exams

Two pipes can fill a tank in 12 minutes and 20 minutes respectively. Both pipes are opened together and after some time the first pipe is closed and the tank is full in totally 10 minutes. For how many minutes was first pipe open?

35 minutes

36 minutes

8 minutes

6 minutes

Explanation:
It is given that two pipes can fill a tank in 12 minutes and 20 minutes respectively.
Tank filled by first pipe in 1 minute =1/12
Tank filled by second pipe in 1 minute =1/20
Tank filled by both pipes in 1 minute = 1/12 + 1/20 =1/10
Let first pipe was open for (10 -x) minutes.
$\dfrac{1}{12} \times (10-x) + \dfrac{1}{20} \times 10 $=1
$\dfrac{10}{12}-\dfrac{x}{12}+\dfrac{1}{2} $ =1
$\dfrac{16}{12} -1 =\dfrac{x}{12} $
$\dfrac{4}{12} =\dfrac{x}{12}$
x=4
Since the first pipe was open for (10-x) minutes,
therefore first pipe was open for 6 minutes.

Additional Questions

Two pipes can fill a tank in 15 minutes and 12 minutes. The outlet pipe can empty the tank in 20 minutes. If all the pipes are opened when, the tank is empty, then in how many minutes will it take to fill the tank?	Answer
Pipe A can fill a tank in 12 hours. Due to a leak at the bottom it takes 20 hours to fill the tank. In what time the leak alone can empty the full tank?	Answer
A cistern can be filled by a tap in 3 hours while it can be emptied by another tap in 8 hours. If both the taps are opened simultaneously, then after how much time will the cistern get filled?	Answer
Two pipes can fill a tank in 20 and 24 minutes respectively and a waste pipe can empty 3 gallons per minute. All the three pipes working together can fill the tank in 15 minutes. The capacity of the tank is:	Answer
A pump can fill a tank with water in 2 hours. Because of a leak, it took 2$ \dfrac{1}{3} $ hours to fill the tank. The leak can drain all the water of the tank in:	Answer
Pipe A can fill a tank in 8 hours, pipe B in 4 hours and pipe C in 24 hours. If all the pipes are open, in how many hours will the tank be filled?	Answer
Pipes A and B can fill a tank in 8 and 24 hours respectively. Pipe C can empty it in 12 hours. If all the three pipes are opened together, then the tank will be filled in:	Answer
Two pipes A and B can fill a tank in 2 and 6 minutes respectively. If both the pipes are used together, then how long will it take to fill the tank?	Answer
A large tanker can be filled by two pipes A and B in 60 minutes and 40 minutes respectively. How many minutes will it take to fill the tanker from empty state if B is used for half the time and A and B fill it together for the other half?	Answer
13 buckets of water fill a tank when the capacity of each bucket is 51 litres. How many buckets will be needed to fill the same tank, if the capacity of each bucket is 17 litres?	Answer

Share with Friends