Multiple choice

A tank can be filled by two taps A and B is in 25 minutes and 30 minutes respectively can be emptied by a third in 15 minutes. If al the taps are turned on at the same moment, what part of the cistern will remain unfilled at the end of 100 minutes.

  1. 1/3

  2. 1/4

  3. 2/4

  4. 2/3

  5. 1/5
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In 1 minute: Tap A fills 1/25, Tap B fills 1/30, Tap C empties 1/15. Net rate = 1/25 + 1/30 - 1/15 = (6+5-10)/150 = 1/150. In 100 minutes: 100 × (1/150) = 2/3 filled. So unfilled = 1 - 2/3 = 1/3. The question asks what part remains UNFILLED, which is 1/3.

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