An alloy of copper and bronze weight 50g. It contains 80% Copper. How much copper should be added to the alloy so that percentage of copper is increased to 90%?

• A. 60 gm
• B. 55 gm
• C. 45 gm
• D. 50 gm

Answer: (D)

Initial quantity of copper = 80 100   x   50 = 40 g  And that of Bronze = 50 - 40 = 10 g Let 'p' gm of copper is added to the mixture => 50   +   p   x   90 100 = 40 + p => 45 + 0.9p = 40 + p => p = 50 g Hence, 50 gms of copper is added to the mixture, so that the copper is increased to 90%.