Multiple choice

A cistern usually can be filled by a tap in 15 hrs but due to a leak in the bottom it takes 3 hrs more to fill. If the tank is half filled find, in how many hours leak will empty it.

  1. 24

  2. 25

  3. 30

  4. 45

  5. None of these
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Tap fills in 15 hr, so fill rate = C/15 per hr. With leak, fills in 18 hr, so net rate = C/18. Leak rate = C/15 - C/18 = C/90 per hr. Time for leak to empty full tank = 90 hr. For half-filled tank (C/2), time = (C/2)/(C/90) = 45 hr.

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