Question

Two pipes a and b can fill a tank in 20 and 25 seconds respectively. both are opened at the same time and after 5 minutes the first one is closed. how much more time will it take for the tank to be full?

Answer 1

1st tank takes 20 sec to fill and second tank takes 25 sec then 1st tank takes 20 min to fill the tank then second tank takes 5 min and 5 sec means 305 sec