Question 711594
Pure silver is 100% silver.

There are high percent silver and lower percent silver and the mixture will make some intermediate percent silver, T.

T = the resulting % silver Unknown but will be found
H = 100, the pure silver 100%
L = 10, the 10% silver concentration
x = 70 ounces of 10% silver
y = 20 ounces of 100% silver.


Objective is find T.  

Amount of silver = x*L+y*H
Amount of alloy = x+y


{{{T=(x*L+y*H)/(x+y)}}}


Use the given values:
{{{T=(70*10+20*100)/(70+20)}}}
T=30,  so alloy resulting is 30% silver.