Chapter 6 - Systems of Equations and Inequalities - 6-4 Application of Linear Systems - Practice and Problem-Solving Exercises - Page 386: 10

16 kg of 20% copper and 64 kg of 60% copper

$x+y=80$ $.2x+.6y=.52(80)$ $x+y-y=80-y$ $x=80-y$ $.2x+.6y=.52(80)$ $.2*(80-y)+.6y=41.6$ $16-.2y+.6y=41.6$ $16+.4y-16=41.6-16$ $.4y = 25.6$ $.4y/.4 = 25.6/.4$ $y=64$ $x = 80-y$ $x=80-64$ $x=16$