Question 201648
<font face="Garamond" size="+2">

By itself, the drain can empty *[tex \Large \frac{1}{30}] of the tank in 1 minute.  By itself, the inlet can fill *[tex \Large \frac{1}{45}] of the tank in 1 minute.

Since filling takes longer than emptying, the net effect is that the tank will empty itself, so with both valves open,

*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{1}{30} - \frac{1}{45}]

of the tank will empty in one minute, and it will then take

*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{1}{\frac{1}{30} - \frac{1}{45}}]

minutes for the tank to empty.  You get to do the arithmetic.  Hint: LCD = 90.

John
*[tex \LARGE e^{i\pi} + 1 = 0]
</font>