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- Find each pipe's rate.
- Add filling rates and subtract emptying rates.
- Invert the net rate to get time.
Correct Answer: A
Correct Answer: A
Method / Topic: Pipes and Cisterns
The answer uses the net filling rate.
Short Explanation
Detailed Explanation
Correct Answer: A
Method / Topic: Pipes and Cisterns
The first pipe fills 1/3 in 4 hours, leaving 2/3. Together the rate is 1/12+1/18=5/36, so remaining time=(2/3)÷(5/36)=4.8 hours; total=8.8 hours.
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Learn + Solve: Shortcut, Trap & Fast Route Click to view shortcut, steps, and common mistake
Shortcut used, common trap, and the fastest solving route
- Find each pipe's rate.
- Add filling rates and subtract emptying rates.
- Invert the net rate to get time.
A pipe fills a tank in 12 hours. After it works alone for 4 hours, a second pipe that fills the tank in 18 hours is opened. How much total time is needed to fill the tank?
Explanation
Correct Answer: A
Method / Topic: Pipes and Cisterns
The answer uses the net filling rate.
Short Explanation
Detailed Explanation
Correct Answer: A
Method / Topic: Pipes and Cisterns
The first pipe fills 1/3 in 4 hours, leaving 2/3. Together the rate is 1/12+1/18=5/36, so remaining time=(2/3)÷(5/36)=4.8 hours; total=8.8 hours.
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