Question

A tap can fill a cistern in 15 min and other can empty it in 18 min .Find in how many minute the tank will be filled up

Answer 1

Answer

90 min

Step-by-step explanation:

First tap can fill it in 15 min

Second tap can empty it in 18 min

So the work done by the first pipe in 1 min will be 1/15

Similarily, work done by second pipe in 1 min will be 1/18

Total work done by both the pipes in 1 min = 1/15 - 1/18 ( - 1/18 since the second pipe is working against first pipe)

= 1/90

If the work done in one minute is 1/90

Then the total time taken will be the reciprocal of 1/90, i.e 90 min

Hope this helps you out :)

Answer 2

Answer:

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

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

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

solution:-

1/15-1/18=1/90

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

HOPE ITS HELP YOU.