Question

Find the rate of money collected per sweatshirt sold.

Answer 1

$\bf \cfrac{shirts}{price}\qquad \cfrac{3}{60},\cfrac{5}{100},\cfrac{8}{160},\cfrac{9}{180},\cfrac{12}{240}\implies \begin{array}{|c|ccccc|cc} \cline{1-6} x&3&5&8&9&12\\ \cline{1-6} y&60&100&160&180&240\\ \cline{1-6} \end{array}$

so let's pick two points off that shirts/price table, say 5,100 and 9,180

$\bf (\stackrel{x_1}{5}~,~\stackrel{y_1}{100})\qquad (\stackrel{x_2}{9}~,~\stackrel{y_2}{180}) \\\\\\ slope = m\implies \cfrac{\stackrel{rise}{ y_2- y_1}}{\stackrel{run}{ x_2- x_1}}\implies \cfrac{180-100}{9-5}\implies \cfrac{80}{4}\implies \stackrel{\textit{average rate of change}}{\cfrac{20}{1}\implies \stackrel{\downarrow }{20}}$