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

Pipe A can fill a tank in 18 minutes, while pipe B can empty the completely filled tank in 27 minutes. Initially, pipe A is opened and after 6 minutes pipe B is also opened. In how much time (in minutes) will the remaining tank be filled completely?

A
36
B
32
C
35
D
21
Result Summary
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NTPC Graduate Tier 1
2025 • 06 Jun, 2025 • Shift-2
Pipe A can fill a tank in 18 minutes, while pipe B can empty the completely filled tank in 27 minutes. Initially, pipe A is opened and after 6 minutes pipe B is also opened. In how much time (in minutes) will the remaining tank be filled completely?
Correct Answer
36
Capacity Calculation: First, determine the total tank capacity by finding the Least Common Multiple (LCM) of 18 and 27, which is 54 units. Thus, Pipe A fills at......
Ref/Book : NTPC Graduate Tier 1 2025
Ref. Subject Mathematics
Chapter -
Ref. Topic Time and Work
Pg. No -
💡 Analysis & Explanation
Capacity Calculation ▼
First, determine the total tank capacity by finding the Least Common Multiple (LCM) of 18 and 27, which is 54 units. Thus, Pipe A fills at +3 units/min, and Pipe B empties at -2 units/min.
Initial Phase Analysis ▼
Pipe A operates alone for the first 6 minutes. It fills 3 × 6 = 18 units. The remaining empty portion of the tank is 54 - 18 = 36 units.
Combined Efficiency ▼
Once Pipe B is opened, both pipes operate simultaneously. The net filling rate becomes 3 - 2 = 1 unit per minute.
Final Time Computation ▼
To fill the remaining 36 units at a net rate of 1 unit/min, it will clearly take 36 / 1 = 36 minutes.
Conclusion ▼
The remaining tank takes 36 minutes to fill.
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