Question

A cistern can be filled by one tap in 4 hrs. and another tap in 6 hrs. How long will it take to fill the
cistern if both taps are opened together?
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Answer 1

Step-by-step explanation:

The first tap fills in 4 hours, so it fills at the rate of 1/4 or 6/24 of the tank each hour.

The second tap fills in 6 hours, so it fills at the rate of 1/6 or 4/24 of the tank each hour.

Together they fill at the rate of 6/24 + 4/24 of the tank each hour or 10/24 or 5/12 of the tank each hour.

Therefore it will take 12/5 hours or 2 and 2/5 hours to do the job, or 2 hours 24 minutes.