Multiple choice

Two pipes can independently fill a bucket in 20 minutes and 25 minutes. Both are opened together for 5 minutes after which the second pipe is turned off. What is the time by the first pipe alone to fill the remaining portion of the bucket?

  1. 11 minutes

  2. 16 minutes

  3. 20 minutes

  4. 15 minutes

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Pipe A rate = 1/20 bucket/min, Pipe B rate = 1/25 bucket/min. Combined rate = 1/20 + 1/25 = 9/100 bucket/min. In 5 minutes, they fill 5 × 9/100 = 9/20 of bucket. Remaining = 11/20. Pipe A alone takes (11/20) ÷ (1/20) = 11 minutes.