Q1.
Pipe A can fill a tank in 10 hours and Pipe B can fill it in 15 hours. If both pipes are opened together, how much time will they take to fill the tank?
- 5 hours
- 6 hours
- 7 hours
- 8 hours
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Answer: B. 6 hours
Combined rate is (¹⁄₁₀ + ¹⁄₁₅) = ¹⁄₆, so time taken is 6 hours.
Q2.
A tap can fill a tank in 8 hours. Another tap can empty it in 12 hours. If both taps are opened simultaneously, in how many hours will the tank be full?
- 24 hours
- 20 hours
- 16 hours
- 18 hours
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Answer: A. 24 hours
Net filling rate is (¹⁄₈ - ¹⁄₁₂) = ¹⁄₂₄, so time taken is 24 hours.
Q3.
Pipe P can fill a tank in 12 minutes, Pipe Q in 15 minutes, and Pipe R can empty it in 20 minutes. If all three pipes are opened together, in what time will the tank be filled?
- 8 minutes
- 9 minutes
- 10 minutes
- 12 minutes
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Answer: C. 10 minutes
Combined rate is (¹⁄₁₂ + ¹⁄₁₅ - ¹⁄₂₀) = ¹⁄₁₀, so time taken is 10 minutes.
Q4.
A pipe can fill a tank in 6 hours. After half the tank is filled, three more similar pipes are opened. What is the total time taken to fill the tank completely?
- 3 hours 30 minutes
- 4 hours
- 4 hours 15 minutes
- 3 hours 45 minutes
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Answer: D. 3 hours 45 minutes
First ½ tank takes 3 hours. Remaining ½ tank by 4 pipes takes (½) ÷ (⁴⁄₆) = ¾ hours. Total 3 hours 45 minutes.
Q5.
A tank can be filled by a tap in 4 hours. Due to a leak in the bottom, it takes 6 hours to fill the tank. If the tank is full, how much time will the leak take to empty it?
- 10 hours
- 12 hours
- 14 hours
- 8 hours
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Answer: B. 12 hours
Leak's emptying rate is (¹⁄₄ - ¹⁄₆) = ¹⁄₁₂, so the leak empties in 12 hours.
Q6.
Two pipes A and B can fill a tank in 20 minutes and 30 minutes respectively. If both pipes are opened together, but pipe A is closed after 10 minutes, how much more time will pipe B take to fill the remaining tank?
- 6 minutes
- 7 minutes
- 5 minutes
- 8 minutes
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Answer: C. 5 minutes
Work done in 10 min is ¹⁰⁄₁₂ = ⁵⁄₆. Remaining ¹⁄₆ by B takes (¹⁄₆) ÷ (¹⁄₃₀) = 5 minutes.
Q7.
Pipe A is twice as fast as pipe B in filling a tank. If B can fill the tank in 30 minutes, how much time will they take to fill the tank together?
- 12 minutes
- 15 minutes
- 8 minutes
- 10 minutes
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Answer: D. 10 minutes
A's rate is ¹⁄₁₅, B's rate is ¹⁄₃₀. Combined rate is (¹⁄₁₅ + ¹⁄₃₀) = ¹⁄₁₀, so 10 minutes.
Q8.
A pipe fills a tank in 16 hours. After 4 hours, it is found that a leak has developed in the tank. If the leak can empty the full tank in 24 hours, in what time will the remaining tank be filled?
- 36 hours
- 32 hours
- 40 hours
- 44 hours
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Answer: A. 36 hours
In 4 hours, ¹⁄₄ tank filled. Net rate with leak is (¹⁄₁₆ - ¹⁄₂₄) = ¹⁄₄₈. Remaining ¾ tank takes (¾) ÷ (¹⁄₄₈) = 36 hours.
Q9.
Two pipes P and Q can fill a tank in 12 hours. If pipe P alone can fill the tank in 18 hours, how long will pipe Q alone take to fill the tank?
- 30 hours
- 36 hours
- 40 hours
- 45 hours
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Answer: B. 36 hours
Q's rate = (¹⁄₁₂ - ¹⁄₁₈) = ¹⁄₃₆, so Q takes 36 hours.
Q10.
A tank has two inlet pipes. The first pipe can fill the tank in 3 hours and the second pipe can fill it in 4 hours. If the first pipe is opened for 1 hour and then closed, and the second pipe is opened, how much more time will the second pipe take to fill the remaining tank?
- 2 hours 30 minutes
- 2 hours 45 minutes
- 2 hours 40 minutes
- 3 hours
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Answer: C. 2 hours 40 minutes
First pipe fills ¹⁄₃ in 1 hour. Remaining ²⁄₃ filled by second pipe at ¹⁄₄ rate takes (²⁄₃) ÷ (¹⁄₄) = ⁸⁄₃ hours = 2 hours 40 minutes.
