Question 202147
A silversmith mixed 25g of a 70% silver alloy with 50g of a 15% silver alloy. What is the percent concentration of the resulting mixture? 
I have set up .70(25) + .15(50) but I know I am missing part of the equation. 
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That gives you the amount of silver.
.7*25 + .15*50 = 17.5 + 7.5 = 25 gm of Ag
The total alloy is  75 gm
25/75 = 1/3 = ~ 33% silver