Question 987996
Let x = the fraction of the gold alloy.  Then 1-x will be the fraction of the copper alloy.
So we can write the following equation:
19x + 9(1-x) = 12
Solve for x:
10x = 3
x = 3/10 = 0.3
1-x = 0.7
So the proportion is 7:3 copper to gold