Multiple choice

A cistern can be filled in 9 hours. But due to a leak, it takes one hour more. If the cistern is full, in what time will it become empty due to the leak?

  1. 75 hours

  2. 60 hours

  3. 30 hours

  4. 90 hours
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Fill pipe rate = 1/9 cistern/hour. With leak: rate = 1/10 cistern/hour. Leak rate = 1/9 - 1/10 = (10-9)/90 = 1/90 cistern/hour (leak empties). So full cistern empties in 90 hours by leak alone. Answer D is correct.

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