This question was dropped by NTA (a work-and-time problem on pumps), so all candidates were awarded marks. 6 pumps working 12 hours a day empty a tank in 15 days. How many hours a day should 8 pumps work to empty the tank in 9 days?
A13 hours
B14 hours
C15 hours ✓ Correct
D16 hours
Correct answer: (C) 15 hours
Explanation
The 8 pumps must run 15 hours a day.
Total pump-hours are fixed: pumps x hours/day x days.
6 x 12 x 15 = 1080 pump-hours empty the tank.
With 8 pumps over 9 days there are 8 x 9 = 72 pump-days.
Hours per day = 1080 / 72 = 15.
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