Ametalworker has a metal alloy that is 15% copper and another alloy that is 75% copper. how many kilograms of each alloy should the metal worker combine to create 90 kilograms of a 51% copper alloy?

X - the mass of the first alloy (15%)
y - the mass of the second alloy (75%)

x kg of the first alloy contains 15%x=0.15x=(15/100)x=(3/20)x kg of copper
y kg of the second alloy contains 75%y=0.75y=(75/100)y=(3/4)y kg of copper
90 kg of a 51% copper alloy contains 51%*90=0.51*90=45.9 kg of copper



The metal worker should combine 36 kg of the 15% copper alloy and 54 kg of the 75% copper alloy to create 90 kilograms of a 51% copper alloy.