let [A] be a 3x3 matrix with percentages of copper, tin, and cadmium for each alloy

let [B] be a 3x1 matrix of the unknown resistances of each individual metal

let [C] be a 3x1 matrix of the measured resistance of each alloy

[A][B] = [C]

solve for matrix [B]

My calculator sez the resistances for copper, tin, and cadmium to be .0056, .0076, and .0036 ohms respectively.