Question 219587
<font face="Garamond" size="+2">


Let *[tex \Large x] represent the number of hours it takes Sally to paint the house.  Let *[tex \Large y] represent the number of hours it takes John to paint the house.


If Sally can paint the house in *[tex \Large x] hours, she can paint *[tex \Large \frac{1}{x}] of the house in one hour.  Likewise, John can paint *[tex \Large \frac{1}{y}] of the house in one hour.  So given both working together, the house will get painted at a rate of:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{1}{x}\ +\ \frac{1}{y}\ =\ \frac{y + x}{xy}] of the house per hour.


Therefore the entire house will be painted in:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ \frac{1}{\frac{y + x}{xy}}\ =\ \frac{xy}{y+x}] hours.


Just plug in the values you were given and do the arithmetic.  


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