Question

You might need: Calculator Problem Heather is a cashier. She can ring up 12 customers in 9 minutes. At this rate, how many minutes does it take her to ring up 4 customers?

Answer 1

$\bf \begin{array}{ccll} customers&minutes\\ \cline{1-2} 12&9\\ 4&x \end{array}\implies \cfrac{12}{4}=\cfrac{9}{x}\implies \cfrac{3}{1}=\cfrac{9}{x} \\\\\\ 3x=9\implies x=\cfrac{9}{3}\implies x=3$