Question

A tap can fill a cistern in 15 minutes and another can empty it in 18 minutes.Find in how many minutes the tank will be filled up?

Answer 1

Answer:

15+18

Step-by-step explanation:

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Answer 2

Step-by-step explanation:

In 1min the 1st tap can fill =1/15 of the cistern.

in 1min the 2nd tap can empty=1/18 of the cistern.

so,in 1min the tank will filled up (1/15-1/18)of the cistern.(negative- is there as second tap empty it.)

solution:-

1/15-1/18=1/90.

therefore, the tank will be filled up in 1÷1/90=90 mins.

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