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NTPC Graduate Tier 1 2025 Shift-2 📅 06 Jun, 2025

One pipe can fill the tank in 9 minutes while another pipe can empty completely filled tank in 90 minutes. If both the pipes are operated together on empty tank, how long (in minutes) will it take to fill half of the tank?

A
5
B
10
C
6
D
11
Result Summary
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NTPC Graduate Tier 1
2025 • 06 Jun, 2025 • Shift-2
One pipe can fill the tank in 9 minutes while another pipe can empty completely filled tank in 90 minutes. If both the pipes are operated together on empty tank, how long (in minutes) will it take to fill half of the tank?
Correct Answer
5
Individual Rates: The filling pipe works at a positive rate of +1/9 of the tank per minute. The emptying pipe works at a negative rate of -1/90 of the tank per ......
Ref/Book : NTPC Graduate Tier 1 2025
Ref. Subject Mathematics
Chapter -
Ref. Topic Time & Work
Pg. No -
💡 Analysis & Explanation
Individual Rates ▼
The filling pipe works at a positive rate of +1/9 of the tank per minute. The emptying pipe works at a negative rate of -1/90 of the tank per minute.
Combined Efficiency ▼
When operating simultaneously, their net combined rate is (1/9) - (1/90). Converting to a common denominator gives (10/90) - (1/90) = 9/90.
Simplification ▼
The net rate is 1/10 per minute, meaning it takes 10 full minutes to completely fill the entire tank.
Conclusion ▼
To fill exactly half of the tank, it will logically take 10 / 2 = 5 minutes.
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