Chapter 1 - Equations and Inequalities - 1.2 Applications and Modeling with Linear Equations - 1.2 Exercises - Page 100: 5

There are $90$ liters of pure acid in the 120-liter solution.

Let $x$ = number of liters of solution $y$ = amount of pure acid in the solution Note that $75\%=0.75$. Thus, the amount of pure acid in the solution is given by the equation: $y=0.75x$ Therefore, in a 120-liter solution, the amount of pure acid is: $y=0.75x \\y=0.75(120)$ $\\y=90$ liters