Pipes and cisterns
Ten quantitative aptitude questions, each marked as you answer.
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Pipe A fills a tank in 7 hours; pipe B empties the full tank in 14 hours. If both are opened together on an empty tank, when will it be full?
Answer and working
Answer D
Net filling per hour = 1/7 − 1/14 = 1/14. Time = 14 hours.
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Two taps can fill a cistern in 12 minutes and 36 minutes respectively. If both are opened together, how long will it take to fill the cistern?
Answer and working
Answer D
Together per minute: 1/12 + 1/36 = 1/9. Time = 12 × 36 ÷ 48 = 9 minutes.
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Pipe A fills a tank in 24 hours; pipe B empties the full tank in 60 hours. If both are opened together on an empty tank, when will it be full?
Answer and working
Answer B
Net filling per hour = 1/24 − 1/60 = 1/40. Time = 40 hours.
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Two taps can fill a cistern in 15 minutes and 60 minutes respectively. If both are opened together, how long will it take to fill the cistern?
Answer and working
Answer A
Together per minute: 1/15 + 1/60 = 1/12. Time = 15 × 60 ÷ 75 = 12 minutes.
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Two taps can fill a cistern in 18 minutes and 36 minutes respectively. If both are opened together, how long will it take to fill the cistern?
Answer and working
Answer D
Together per minute: 1/18 + 1/36 = 1/12. Time = 18 × 36 ÷ 54 = 12 minutes.
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Pipe A fills a tank in 22 hours; pipe B empties the full tank in 44 hours. If both are opened together on an empty tank, when will it be full?
Answer and working
Answer D
Net filling per hour = 1/22 − 1/44 = 1/44. Time = 44 hours.
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Pipe A fills a tank in 10 hours; pipe B empties the full tank in 20 hours. If both are opened together on an empty tank, when will it be full?
Answer and working
Answer D
Net filling per hour = 1/10 − 1/20 = 1/20. Time = 20 hours.
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Pipe A fills a tank in 12 hours; pipe B empties the full tank in 30 hours. If both are opened together on an empty tank, when will it be full?
Answer and working
Answer B
Net filling per hour = 1/12 − 1/30 = 1/20. Time = 20 hours.
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Pipe A fills a tank in 6 hours; pipe B empties the full tank in 8 hours. If both are opened together on an empty tank, when will it be full?
Answer and working
Answer B
Net filling per hour = 1/6 − 1/8 = 1/24. Time = 24 hours.
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Pipe A fills a tank in 8 hours; pipe B empties the full tank in 9 hours. If both are opened together on an empty tank, when will it be full?
Answer and working
Answer C
Net filling per hour = 1/8 − 1/9 = 1/72. Time = 72 hours.
More quantitative aptitude: Percentages, Profit, loss and discount, Simple interest, Compound interest, Ratio and proportion, Averages.