Question 666989
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120 minutes is 2 hours, and 150 minutes is 2.5 hours.  I'm going to use hours because the fraction denominators will be smaller.  If the fill pipe can fill the tank in 2 hours, then the fill pipe can fill *[tex \LARGE \frac{1}{2}] of the tank in 1 hour, and the drain that drains the whole tank in 2.5 hours can drain *[tex \LARGE \frac{2}{5}] of the tank in 1 hour.


Working together, they can fill 


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{1}{2}\ -\ \frac{2}{5}]


of the tank in 1 hour.


Do the arithmetic, then take the reciprocal of the answer to get the number of hours to fill the tank.


John
*[tex \LARGE e^{i\pi}\ +\ 1\ =\ 0]
My calculator said it, I believe it, that settles it
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