Chapter 4 - Section 4.3 - Systems of Linear Equations and Problem Solving - Exercise Set - Page 230: 8

375 ml of 25%, 125 ml of 5 %.

We will call the 5% solution y and the 25% solution x. We first know that there totals must add up to 500 ml: $x+y=500$ Now, we know that the concentration must be 20%. This means: $.25x+.05y=500(.2)$ $.25x+.05y=100$ We now substitute to find: $.25(500-y)+.05y=100$ $125-.2y=100$ $y = 125$ We now find: $ x = 500-y = 500 - 125 = 375 ml$