Question

3. Two pipes A and B can separately fill a cistern in 15 hours and 20 hours respectively. There is a third pipe at the bottom to empty it. If all the three pipes are simultaneously opened, then the cistern is filled in 30 hours. In how much time the third pipe alone can empty the cistern?

Answer please!...​

Answer 1

Answer:

100 minutes

Let the third pipe empty the cistern in x minutes.

Part of cistren filled in 1 minute when all three pipes are opened simultaneously

= \frac{1}{60} + \frac{1}{75} - \frac{1}{x}

According to the question,

= \frac{1}{60} + \frac{1}{75} - \frac{1}{x} = \frac{1}{50}

=> \frac{1}{x} = \frac{1}{60} + \frac{1}{75} - \frac{1}{50}

=>\frac{5+4-6}{300}= \frac{3}{300}

=> \frac{1}{x} = \frac{3}{300}

\therefore x = \frac{300}{3} = 100 minutes