Question

a craftsperson has 2 alloys of silver. the 1st one is 70%pure silver amd the second one is 50%. how many kilograms of each must be mixed to have 12kg of an alloy which is 65% silver?

Answer 1

let the amount of 70% silver be x kg
then the amount of 50% silver must be 12-x kg

.7x + .5(12-x) = .65(12)
70x + 50(12-x) = 65(12)

I am sure you can take it from there.
(I got x=9)