A pipe can fill a tank in 3 hours but an outlet B can empty the tank in 10 hours. If both the pipes are opened simultaneously, then the tank will be filled in -

Question: A pipe can fill a tank in 3 hours but an outlet B can empty the tank in 10 hours. If both the pipes are opened simultaneously, then the tank will be filled in -

Solution:
in 1 hour, A fills = 1/3
but B reject = 1/10

so, in 1 hour the net fill-up is = 1/3 - 1/10 = 7/30

hence,
It will take 30/7 hours to fill the tank if both the pipes are opened.