Question 614094
<font face="Times New Roman" size="+2">


In 20 lbs of 20% copper alloy there are 0.2 * 20 = 4 lbs of pure copper.  If you add *[tex \LARGE x] lbs of pure copper, you will have *[tex \LARGE 20\ +\ x] pounds of 50% alloy, of which *[tex \LARGE 0.5(20\ +\ x)] is pure copper.  Since you started with 4 lbs of pure copper, when you are done you will have *[tex \LARGE 4\ +\ x] lbs of pure copper, so:


*[tex \LARGE \ \ \ \ \ \ \ \ \ \ 4\ +\ x\ =\ 0.5(20\ +\ x)]


Solve for *[tex \LARGE x]


John
*[tex \LARGE e^{i\pi}\ +\ 1\ =\ 0]
My calculator said it, I believe it, that settles it
<div style="text-align:center"><a href="http://outcampaign.org/" target="_blank"><img src="http://cdn.cloudfiles.mosso.com/c116811/scarlet_A.png" border="0" alt="The Out Campaign: Scarlet Letter of Atheism" width="143" height="122" /></a></div>
</font>