SOLUTION: A water tank has an inlet pipe and a drain pipe. A full tank can be emptied in 30 minutes if the drain is opened and an empty tank can be filled in 45 minutes with the inlet pipe

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Question 242596: A water tank has an inlet pipe and a drain pipe.
A full tank can be emptied in 30 minutes if the drain is opened and an empty tank can be filled in 45 minutes with the inlet pipe opened.
If both pipes are accidentally opened when the tank is full, then how long will it take to
empty the tank?
Answer by ankor@dixie-net.com(22740) About Me  (Show Source):
You can put this solution on YOUR website!
A water tank has an inlet pipe and a drain pipe.
A full tank can be emptied in 30 minutes if the drain is opened and an empty tank can be filled in 45 minutes with the inlet pipe opened.
If both pipes are accidentally opened when the tank is full, then how long will it take to empty the tank?
:
let t = time (in minutes) to empty with both valves open
:
Let 1 = the completed job (an empty tank)
:
Plus is draining, minus is filling
:
t%2F30 - t%2F45 = 1
Multiply by 90, get rid of the denominators, results:
3t - 2t = 90
t = 90 minutes to empty with both valves open