Question

Two pipes A and B can fill a cistern in 6 minutes and 7 minutes respectively.
Both the pipes are opened alternatively for 1 minute each. In what time will
they fill the cistern?
(Railways, 2006)​

Answer 1

Answer:

In one minute the taps can fill 1/6 and 1/7 of the cistern, respectively. If they are opened alternatively for a minute, they fill 13/42 of the cistern after 2 mins. Therefore total time taken is 6 minutes and 25.7 seconds.