Chapter 11 - Rational Expressions and Functions - 11-6 Inverse Variation - Practice and Problem-Solving Exercises - Page 703: 25

$y = 0.5x$

The values of y seem to vary directly with the values of x. Ratio: $\frac{1}{2}=0.5$ $\frac{2.5}{5}=0.5$ $\frac{4}{8}=0.5$ The ratio $\frac{y}{x}$ is the same for all data pairs. So this is a direct variation equation, and $k =0.5$. The equation is $y = 0.5x$.