use eq. CAg = [(CAgACu) / [(CAgACu) + (CCuAAg)] ] x 100
CAg = 92.5 (wt % of Ag) given
ACu = 63.55 g/mol (atomic weight of Cu) tables
CCu = 7.5 (wt % of Cu) given
AAg = 107.87 g/mol (atomic weight of Ag) tables
CAg =[ [(92.5)(63.55)] / [(92.5)(63.55) + (7.5)(107.87)] ]x 100 = 87.9%
CCu = [(CCuAAg ) / [(CAgACu) + (CCuAAg)]] x 100
CCu =[ [(7.5)(107.87)] / [(92.5)(63.55) + (7.5)(107.87)]] x100 = 12.1%
The easiest way is to find one of the solutions and subtract that from 100. Because there can only be 100 %.
If we find CAg = 87.9%, then CCu would be 1 - 87.9 = 12.1%
From at% to wt%
C
Ag = [C
AgA
Ag / (C
AgA
Ag + C
CuA
Cu)] x 100
= [(87.9)(107.87) / [(87.9)(107.87) + (12.1)(63.55)]] x 100 = 92.5
CCu = [CCuACu / (CCuACu + CAgAAg)] x 100
= [(12.1)(63.55) / [(12.1)(63.55) + (87.9)(107.87)]] x 100 = 7.5