Chapter 9 - 9.2 - Two Variable Linear Systems - 9.2 Exercises - Page 647: 50a

$x+y=500 \\ 0.87 x+0.92 y=445$

Let $x$ and $y$ be the number of gallons of 87-octane gasoline and of 92-octane gasoline, respectively. $x+y=500 \\ 0.87 x+0.92 y=(0.89)(500)$ Therefore, the system of two equations is: $x+y=500 \\ 0.87 x+0.92 y=445$