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Time and Work
Pipes and Cisterns
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RRB NTPC Graduate Tier 1 2025 Shift-3 📅 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 the tank completely?

A
13
B
11
C
12
D
10
Result Summary
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APEDIA

RRB NTPC Graduate Tier 1
2025 • 06 Jun, 2025 • Shift-3
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 the tank completely?
Correct Answer
10
Work Rates: The filling pipe fills $1/9$ of the tank per minute. The emptying pipe empties $1/90$ of the tank per minute.Combined Rate Calculation: When both op......
Ref/Book : RRB NTPC Graduate Tier 1 2025
Ref. Subject Time and Work
Chapter -
Ref. Topic Pipes and Cisterns
Pg. No -
💡 Analysis & Explanation
Work Rates ▼
The filling pipe fills $1/9$ of the tank per minute. The emptying pipe empties $1/90$ of the tank per minute.
Combined Rate Calculation ▼
When both operate together, their net filling rate per minute is $(1/9) - (1/90) = (10 - 1) / 90 = 9/90 = 1/10$.
Total Time Calculation ▼
Since the net rate is $1/10$ of the tank per minute, it will take 10 minutes to fill the entire tank.
Conclusion ▼
It will take 10 minutes to fill the empty tank completely.
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