An alloy contains tin and copper in the ratio 4 : 5. If tin has 20% impurity and copper 58%, what is the average % impurity?

41.1%

Ratio of alloy contains tin and copper = 4 : 5 or = 400x : 500x

Total quantity of impurity in tin = 400x × (\(\frac{20}{100}\)) = 80x

Total quantity of impurity in copper = 500x × (\(\frac{58}{100}\)) = 290x

Total quantity of impurity = 80x + 290x = 370x

Required percentage = (\(\frac{370x}{900x}\)) × 100 = 41.1%