Question 1053962
Let n be the amount of time taken to fill the tank. If all 3 pumps are going at the same time, then:
n/50 + n/60 -n/75=1 (The third pump DRAINS the tank.)
So:
6n/300 + 5n/300 - 4n/300=1
7n=300
n=300/7
It will take 300/7 minutes to fill the tank. ☺☺☺☺