Solved UPSC CDS/OTA Question
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Q · Time and WorkMedium · 45s
Two inlet pipes can fill a tank in 15 hours and 20 hours respectively. A third outlet pipe can empty it in 30 hours. If all three are opened together, how long will it take to fill the tank?
TopicTime and Work
Question Typemultiple choice
DifficultyMedium
Marking+1 / −0.25
Test Duration30 min
Step-by-Step Solution
The complete worked solution.
Every step explained — no skipped algebra.
Net rate = 1/15 + 1/20 - 1/30 = (4+3-2)/60 = 5/60 tank/hour → Time = 60/5 = 12 hours.
Final Answer: Option A — 10 hours