<PRE><B>Question 329130</B>
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 i t take to empty the tank?
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Let t = time it takes to empty tank
then
1 - t(1/30) + t(1/45) = 0
1 - t/30 + t/45 = 0
multiplying both sides by (30)(45):
1350 - 45t + 30t = 0
1350 - 15t = 0
1350 = 15t
90 minutes = t
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