Question

pipe A can empty a filled tank in 20 hours while pipe B can fill the same tank when empty in 35 hour if alternately pipes a and b are turned on for an hour each time starting when the tank is full how long will it take to empty the tank​

Answer 1

time taken to empty the tank=1/20-1/35

=(7-5)/140=2/140=1/70

=70 hours will be taken to empty the tank