A goldsmith has two gold alloys. The first alloy is 30% gold; the second alloy is 80% gold. How many grams of each should be mixed to produce 10 grams of an alloy that is 40% gold?

Question

amount of 30% gold ___ g
amount of 80% gold ___ g

Answer 1

.3 a + .8 b = .4 * 10
a + b = 10

.3 a + .8 b = 4
.8 a + .8 b = 8
---------------- subtract
-.5 a = - 4

a = 8
so b = 2