Question 703038
Higher concentration and lower concentration available; known quantity of mixture desired.

Key idea is (quantity of gold)/(quantity of mix)=(fraction as gold)


a= quantity of higher concentration alloy to use (unknown)
b= quantity of lower concentration alloy to use  (unknown)
P_sub_a = percent gold in a, 0.30
P_sub_b = percent gold in b, 0.10
F = the FRACTION of the desired alloy which is gold.  0.15


{{{(a*P[a]+b*P[b])/(a+b)=F}}}
{{{a+b=4}}}
Two equations and two unknowns.  Solve for a and b.