gold alloy problem

https://www.assignmentexpert.com/homework-answers/mathematics/algebra/question-32394


Question 987996: Gold and copper are heavier than water by 19 and 9 times respectively. In what proportion should they be mixed to form an alloy so that it will be heavier than water by 12 times?

Answer by htmentor(1029) About Me  (Show Source):
You can put this solution on YOUR website!
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