Multiple choice

A tank usually can be filled by a tap A in 15 hrs but it can fill the tank with the help of tap B in 10 hrs. If the cistern is half filled , then in how many hours tap B will fill it.

  1. 20

  2. 25

  3. 10

  4. 15

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

Tap A rate = 1/15 tank per hour. Combined A + B rate = 1/10 tank per hour. So B's rate = 1/10 - 1/15 = (3 - 2)/30 = 1/30 tank per hour. B fills full tank in 30 hours, so half tank in 15 hours.

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