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Question

Pipe A can fill an empty tank in 18 hours and pipe B can fill the same empty tank in 24 hours. If both the pipes are opened simultaneously, how much time (in hours) will they take to fill the empty tank?

This question was previously asked in
SSC CGL 2023 (Tier-II) Paper 1 Previous Year Paper (26-Oct-2023) (Shift-1)
The correct answer is \(10\frac{2}{7}\)

Calculating Combined Pipe Filling Time

This problem involves calculating the time it takes for two pipes, A and B, working together to fill an empty tank. We are given the individual times each pipe takes to fill the tank.

Understanding Pipe Filling Rates

To solve this, we first determine the rate at which each pipe fills the tank. The rate is the fraction of the tank filled per hour.

  • Pipe A fills the tank in 18 hours. So, the rate of Pipe A is $\frac{1}{18}$ of the tank per hour.
  • Pipe B fills the tank in 24 hours. So, the rate of Pipe B is $\frac{1}{24}$ of the tank per hour.

Calculating Combined Filling Rate

When both pipes are opened simultaneously, their rates add up. We need to find the combined rate:

Combined Rate = Rate of Pipe A + Rate of Pipe B

Combined Rate = $ \frac{1}{18} + \frac{1}{24} $

To add these fractions, we find a common denominator. The least common multiple (LCM) of 18 and 24 is 72.

Combined Rate = $ \frac{1 \times 4}{18 \times 4} + \frac{1 \times 3}{24 \times 3} $

Combined Rate = $ \frac{4}{72} + \frac{3}{72} $

Combined Rate = $ \frac{4 + 3}{72} $

Combined Rate = $ \frac{7}{72} $ of the tank per hour.

Determining Total Time Taken Together

The time taken to fill the tank together is the reciprocal of the combined rate.

Time = $ \frac{1}{\text{Combined Rate}} $

Time = $ \frac{1}{\frac{7}{72}} $

Time = $ \frac{72}{7} $ hours.

Converting Time to Mixed Fraction

To express the answer in the format given in the options, we convert the improper fraction $ \frac{72}{7} $ to a mixed number:

Divide 72 by 7:

$ 72 \div 7 = 10 $ with a remainder of $ 2 $.

So, $ \frac{72}{7} $ hours is equal to $ 10\frac{2}{7} $ hours.

Final Answer Analysis

The time calculated, $ 10\frac{2}{7} $ hours, matches one of the options provided.

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Similar Questions

  1. An inlet pipe can fill an empty tank in 140 hours while an outlet pipe drains a completely-filled tank in 63 hours. If 8 inlet pipes and y outlet pipes are opened simultaneously, when the tank is empty, then the tank gets completely filled in 105 hours. Find the value of y.

  2. There are two inlet pipes A and B connected to a tank. A and B can fill the tank in 32 h and 28 h, respectively. If both the pipes are opened alternately for 1 h, starting with A, then in how much time (in hours, to nearest integer) will the tank be filled?

  3. Two pipes A and B can fill an empty tank in 10 hours and 16 hours respectively. They are opened alternately for 1 hour each, opening pipe B first, in how many hours, will the empty tank be filled?

  4. Pipes A and B can fill a tank in 12 hours and 16 hours respectively and pipe C can empty the full tank in 24 hours. All three pipes are opened together, but after 4 hours pipe B is closed. In how many hours, the empty tank will be completely filled?

  5. Pipes A, B and C can fill a tank in 20, 30 and 60 hours, respectively. Pipes A, B and C are opened at 7 a.m., 8 a.m., and 9 a.m., respectively, on the same day. When will the tank be full?

  6. An inlet pipe can fill an empty tank in \(4\frac{1}{2}\) hours while an outlet pipe drains a completely filled tank in \(7\frac{1}{5}\) hours. The tank is initially empty. and the two pipes are alternately opened for an hour each, till the tank is completely filled, starting with the inlet pipe. In how many hours will the tank be completely filled? 

  7. Two pipes S1 and S2 alone can fill an empty tank in 15 hours and 20 hours respectively. Pipe S3 alone can empty that completely filled tank in 40 hours. Firstly both pipes S1 and S2 are opened and after 2 hour pipe S3 is also opened. In how much time tank will be completely filled after S3 is opened?  

  8. A pipe can fill a tank in 30 hours. Due to a leakage at the bottom, it is filled in 50 hours. How much time will the leakage take to empty the completely filled tank?

  9. Pipe A and pipe B running together can fill a cistern in 6 minutes. If B takes 5 minutes more than A to fill it, then the time in which A and B will fill that cistern separately will be, respectively, __________ .

  10. There are 3 taps A, B, and C in a tank. These can fill the tank in 10 hours, 20 hours and 25 hours, respectively. At first, all three taps are opened simultaneously. After 2 hours, tap C is closed and A and B keep running. After 4 hours from the beginning, tap B is also closed. The remaining tank is filled by tap A alone. Find the percentage of work done by tap A itself.


Important Questions from Pipe and Cistern

  1. A pipe can fill a cistern in 20 minutes where as the cistern when full can be emptied by a leak in 28 minutes. When both are opened, The time taken to fill the cistern is:

  2. ‘A’ pipe can empty a tank in 20 minutes. The second pipe ‘B’ has a diameter twice as that of ‘A’. If both A & B pipe are attached to the tank how much time will be required to empty the tank?

  3. Pipes A and B can empty a full tank in 16 hours and 24 hours, respectively. Pipe C alone can fill the empty tank in 4 hours. If A, B and C are opened together, the tank will be 35% full after :

  4. Pipes A and B can fill a tank in 36 minutes and 45 minutes, respectively. Both these pipes were opened simultaneously. After 20 minutes, a leak at the bottom of the tank was spotted which was immediately sealed. The tank was full in another 15 minutes. The leak alone can empty the full tank in:

  5. A cistern has a leak which would empty it in 6 hours. A tap is turned on which admits 10 litres of water per minute into the cistern. When it is full it is now emptied in 10 hours. What is the capacity (in litres) of the cistern?

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