college algebra word problem
posted by megan .
A goldsmith has two alloys that are different purities of gold. The first is 3/4 pure and the second is 5/12 pure. How many ounces of each should be melted and mixed in order to obtain a 6 oz mixture that is 2/3 pure gold?

solve
(3/4)x + (5/12)(6x) = (2/3)(6) ,each term times 12
9x + 5(6x) = 48
etc 
Since there are different quantities of each purity wouldn't there be an x and a y in the equation instead of both being x?

Ok,
x + y = 6 > y = 6x
(3/4)x + (5/12)y = (2/3)(6)
sub in the value of y
mmmhhh! 
oooh. okay! thanks!