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Mathematics
Pipes and Cisterns
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NTPC Graduate Tier 1 2025 Shift-2 📅 05 Jun, 2025

One pipe can fill the tank in 10 minutes while another pipe can empty completely filled tank in 20 minutes. If both the pipes are operated together on empty tank, how long (in minutes) will it take to fill the tank completely?

A
22
B
21
C
23
D
20
Result Summary
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NTPC Graduate Tier 1
2025 • 05 Jun, 2025 • Shift-2
One pipe can fill the tank in 10 minutes while another pipe can empty completely filled tank in 20 minutes. If both the pipes are operated together on empty tank, how long (in minutes) will it take to fill the tank completely?
Correct Answer
20
Efficiency of Inlet: The filling pipe accomplishes 1/10th of the total work per minute.Efficiency of Outlet: The emptying pipe drains 1/20th of the total capaci......
Ref/Book : NTPC Graduate Tier 1 2025
Ref. Subject Mathematics
Chapter -
Ref. Topic Pipes and Cisterns
Pg. No -
💡 Analysis & Explanation
Efficiency of Inlet ▼
The filling pipe accomplishes 1/10th of the total work per minute.
Efficiency of Outlet ▼
The emptying pipe drains 1/20th of the total capacity per minute.
Combined Force Dynamics ▼
When running simultaneously, the net volume added per minute is (1/10) - (1/20) = 1/20.
Time Projection ▼
At a net fill rate of 1/20 per minute, filling the entire unit requires the reciprocal time.
Conclusion ▼
It exactly takes 20 minutes to top off the tank.
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