Question 324602
Filling or draining the complete tank is considered as 1 job

filling in 5 hours
so 1/5 of the job in 1 hour.
..
draining in 10 hours
1/10 of the job in 1 hour
..
effective filling when both are open =
1/5 - 1/10 hours
10-5/50= 5/50= 1/10
when both are open
1/10 of the job is done in 1 hour
so it will take 10 hours to fill the tank