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

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Question 175706: a water tank has an inlet pipe and a drain pipe. full tank can be emptied in 30 minutes and if the drain is opened and an empty tank can be filled in 45 mins 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 solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!
If the tank emptys in 30 minutes, then 1%2F30 of the tank empties in 1 minute. Likewise 1%2F45 of the tank fills in 1 minute. So together:

%281%2F30%29+-+%281%2F45%29 of the tank empties in 1 minute.

%283%2F90%29+-+%282%2F90%29

1%2F90 of the tank empties in 1 minute, so it takes 90 minutes for the tank to empty.