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Shortcut used: Convert filling and emptying pipes into one-minute or one-hour work rates.
Solve in 3 steps:
- Find each pipe's rate.
- Add filling rates and subtract emptying rates.
- Invert the net rate to get time.
Common mistake: Do not add an outlet rate as if it fills the tank.
Question 5
Multiple Choice Question
Question
A pipe fills two-fifths of a tank in 4 hours. At the same rate, how long will it take to fill the whole tank?
Explanation
Correct Answer: A
ANSWER
Correct Answer: A
Method / Topic: Pipes and Cisterns
The pipe will fill the tank in 10 hours.
Why this answer is correct
The answer uses the net filling rate.
Short Explanation
The pipe will fill the tank in 10 hours.
Detailed Explanation
Question
A pipe fills two-fifths of a tank in 4 hours. At the same rate, how long will it take to fill the whole tank?
ANSWER
Correct Answer: A
Method / Topic: Pipes and Cisterns
If 2/5 of the tank takes 4 hours, the whole tank takes 4×5/2=10 hours.
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Question 5
Learn + Solve: Shortcut, Trap & Fast Route Click to view shortcut, steps, and common mistake
Learn + solve
Shortcut used, common trap, and the fastest solving route
Shortcut used: Convert filling and emptying pipes into one-minute or one-hour work rates.
Solve in 3 steps:
- Find each pipe's rate.
- Add filling rates and subtract emptying rates.
- Invert the net rate to get time.
Common mistake: Do not add an outlet rate as if it fills the tank.
Question
A pipe fills two-fifths of a tank in 4 hours. At the same rate, how long will it take to fill the whole tank?
Explanation
Correct Answer: A
ANSWER
Correct Answer: A
Method / Topic: Pipes and Cisterns
The pipe will fill the tank in 10 hours.
Why this answer is correct
The answer uses the net filling rate.
Short Explanation
The pipe will fill the tank in 10 hours.
Detailed Explanation
Question
A pipe fills two-fifths of a tank in 4 hours. At the same rate, how long will it take to fill the whole tank?
ANSWER
Correct Answer: A
Method / Topic: Pipes and Cisterns
If 2/5 of the tank takes 4 hours, the whole tank takes 4×5/2=10 hours.
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