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A tank can be filled by a pipe in 9 hours and emptied by another pipe in 18 hour

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Question: A tank can be filled by a pipe in 9 hours and emptied by another pipe in 18 hours. If both pipes are opened together, how long will it take to fill the tank?

Options:

  1. 6 hours
  2. 9 hours
  3. 12 hours
  4. 15 hours

Correct Answer: 12 hours

Solution: 

The net rate is 1/9 - 1/18 = 1/18. Therefore, it will take 18 hours to fill the tank.

A tank can be filled by a pipe in 9 hours and emptied by another pipe in 18 hour

Practice Questions

Q1
A tank can be filled by a pipe in 9 hours and emptied by another pipe in 18 hours. If both pipes are opened together, how long will it take to fill the tank?
  1. 6 hours
  2. 9 hours
  3. 12 hours
  4. 15 hours

Questions & Step-by-Step Solutions

A tank can be filled by a pipe in 9 hours and emptied by another pipe in 18 hours. If both pipes are opened together, how long will it take to fill the tank?
Correct Answer: 18 hours
  • Step 1: Understand that one pipe fills the tank and the other pipe empties it.
  • Step 2: Determine the rate at which the filling pipe works. It fills the tank in 9 hours, so its rate is 1 tank per 9 hours, or 1/9 of the tank per hour.
  • Step 3: Determine the rate at which the emptying pipe works. It empties the tank in 18 hours, so its rate is 1 tank per 18 hours, or 1/18 of the tank per hour.
  • Step 4: Calculate the net rate when both pipes are open. This is done by subtracting the emptying rate from the filling rate: (1/9) - (1/18).
  • Step 5: To subtract these fractions, find a common denominator. The common denominator for 9 and 18 is 18.
  • Step 6: Convert 1/9 to have a denominator of 18: (1/9) = (2/18).
  • Step 7: Now subtract: (2/18) - (1/18) = (1/18).
  • Step 8: The net rate of filling the tank is 1/18 of the tank per hour.
  • Step 9: To find out how long it takes to fill the entire tank, take the reciprocal of the net rate: 1 / (1/18) = 18 hours.
  • Rate of Work – Understanding how to calculate the rate at which work is done when multiple processes are involved, such as filling and emptying a tank.
  • Combined Rates – Learning to combine rates of filling and emptying to find the net effect on the tank's water level.
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