Answer
-3
Work Step by Step
See p.725
The average rate of change of $f(x)$ over the interval $[a, b]$ is $\displaystyle \frac{f(b)-f(a)}{b-a}$
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Given the interval $[1,3]$ and the table,
a=1, $\ \ \ f(1)=5$
b=3, $\ \ \ f(3)=-1$
$\displaystyle \frac{f(b)-f(a)}{b-a} =\displaystyle \frac{-1-5}{3-1}=\frac{-6}{2}=-3$
