Answer:
It take 37.5 hours to fill the tank
Step-by-step explanation:
Given:
Time Taken to fill the tank = 15 hours
Time Taken to empty the tank = 25 hours
To Find:
Time taken to fill the tank when both the inlet and outlet is opened at the same time = ?
Solution:
Let the time to fill the tank be x
In 15 hours the tap fills the tank
Rate at which the tank is filled = 
In 25 hours the tap empties the tank
Rate at which the tank is drained = 
The net gain per minute on the total filling rate is
=>
Rate at which the tank is filled - Rate at which the tank is drained
=>
=>
=>
=> 10x = 375
=>
=>x = 37.5