SOLUTION: A tank can be filled by one inlet pipe in 15 minutes. It takes an outlet pipe 75 minutes to DRAIN the tank. If the outlet pipe is left open, how long will it take to fill the tan

Algebra ->  Rate-of-work-word-problems -> SOLUTION: A tank can be filled by one inlet pipe in 15 minutes. It takes an outlet pipe 75 minutes to DRAIN the tank. If the outlet pipe is left open, how long will it take to fill the tan      Log On


   

Question 118771: A tank can be filled by one inlet pipe in 15 minutes. It takes an outlet pipe 75 minutes to DRAIN the tank. If the outlet pipe is left open, how long will it take to fill the tank?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
A tank can be filled by one inlet pipe in 15 minutes. It takes an outlet pipe 75 minutes to DRAIN the tank. If the outlet pipe is left open, how long will it take to fill the tank?
:
Let x = time required if inlet and drain are both left open
Let the full tank = 1
:
Filling will be positive
Draining will be negative
:
x%2F15 - x%2F75 = 1
:
Multiply equation by 75 to get rid of the denominators:
75*x%2F15 - 75*x%2F75 = 75(1)
:
Cancel out the denominators and you have:
5x - x = 75
:
4x = 75
:
x = 75%2F4
:
x = 18.75 minutes
:
:
Check:
18.75%2F15 - 18.75%2F75 =
1.25 - .25 = 1; confirms our solution