# SOLUTION: I am truly stumped with this one. An alloy weighing 20 kg is 30% copper. How many kg of another alloy, which is 80% copper, must be added in order to produce an alloy which is

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 Question 11749: I am truly stumped with this one. An alloy weighing 20 kg is 30% copper. How many kg of another alloy, which is 80% copper, must be added in order to produce an alloy which is to be 50% copper? Answer by Earlsdon(6294)   (Show Source): You can put this solution on YOUR website!Ok, here we go! First change percentages to decimals: 30% = 0.3 80% = 0.8 50% = 0.5 Now you can set up the equation in which x is the number of Kg. of 80% Cu alloy needed. Simplify and solve for x. Subtract 0.5x from both sides. Subtract 6 from both sides. Now divide both sides by 0.3 13.33... Kg of 80% copper alloy are needed.