Multiple choice

One fill pipe A is 10 times faster than second pipe B. If B can fill a cistern in 66 minutes, then find the time when the cistern will be full if both fill pipes are opened together.

  1. 6 minute

  2. 5 minute

  3. 4 minute

  4. 8 minute

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

Pipe A fills 10 times faster than B, so if B's rate is 1/66 cistern per minute, A's rate is 10/66. Their combined rate is 11/66 = 1/6 cistern per minute, meaning they fill the cistern together in 6 minutes. Option B (5 min) ignores that A alone would take 6.6 minutes, so the combined time cannot be less.