Chapter 1 - Section 1.1 - Introduction to Algebra: Variables and Mathematical Models - Exercise Set - Page 13: 111

$\dfrac{4}{17}$

Let $a=9,$ $b=17,$ and $c=5.$ Since the given formula states that $\dfrac{a}{b}-\dfrac{c}{b}=\dfrac{a-c}{b},$ then \begin{array}{l}\require{cancel} \dfrac{9}{17}-\dfrac{5}{17} \\\Rightarrow \dfrac{9-5}{17} \\\Rightarrow \dfrac{4}{17} .\end{array}