Chapter 4 - Section 4.4 - Systems of Linear Equations and Problem Solving - Exercise Set - Page 322: 44

90 ounces of 10% solution, 30 ounces of 50% solution

10% solution (x) 50% solution (y) 20% solution (120 ounces) $.1*x+.5y=.2*120$ $x+y=120$ $.1*x+.5y=.2*120$ $10*(.1*x+.5y=.2*120)$ $x+5y=240$ $x+y=120$ $x+5y=240$ $x+5y-(x+y)=240-120$ $x+5y-x-y=120$ $4y=120$ $4y/4=120/4$ $y=30$ $x+y=120$ $x+30=120$ $x=90$