Practice Test 8

For $f(x)=2x^2+1$, what is the average rate of change of $f(x)$ from $x=1$ to $x=3$? Use $\frac{f(b)-f(a)}{b-a}$. (Compare the points $(1,f(1))$ and $(3,f(3))$.)

The value of a used laptop (in dollars) is modeled by $V(t)=900-80t$, where $t$ is the number of years since purchase. What is the average rate of change of $V(t)$ from $t=2$ to $t=5$, and what does the sign mean?