You can
put this solution on YOUR website!If first pipe fills the whole tank in 30 minutes, then in one it fills

and if second one empties the tank in 50 minutes then it empties

of tank in one minute. We can write

,this expresses the state of tank after 1 minute.We can subtract and get

=

after 1 minute

of tank will be filled. By dividing 150 by 2 we can determine how long will it take to fill the whole tank.I takes 75 minutes.