csateasy
Two pipes A and B can independently fill a tank completely in 20 and 30 minutes respectively. If both the pipes are opened simultaneously, how much time will they take to fill the tank completely ?
- A.10 minutes
- B.12 minutes
- C.15 minutes
- D.25 minutes
▶ Answer & Explanation
Correct answer: B. 12 minutes
When two pipes work together, their rates of filling are added. Pipe A fills 1/20th of the tank per minute, and Pipe B fills 1/30th of the tank per minute. Together, they fill (1/20 + 1/30) = (3+2)/60 = 5/60 = 1/12th of the tank per minute. Therefore, to fill the entire tank, they will take 12 minutes.
Source: UPSC csat 2015