Question

Walter takes 7/10 of an hour to mow 2/5 of an acre of lawn. At this rate, how many acres will he mow in an hour?

Answer 1

$\bf \begin{array}{ccll} hours&\stackrel{lawn}{acre}\\ \text{\textemdash\textemdash\textemdash}&\text{\textemdash\textemdash\textemdash}\\ \frac{7}{10}&\frac{2}{5}\\\\ 1&a \end{array}\implies \cfrac{\frac{7}{10}}{1}=\cfrac{\frac{2}{5}}{a}\implies \cfrac{\frac{7}{10}}{\frac{1}{1}}=\cfrac{\frac{2}{5}}{\frac{a}{1}}\implies \cfrac{7}{10}\cdot \cfrac{1}{1}=\cfrac{2}{5}\cdot \cfrac{1}{a} \\\\\\ \cfrac{7}{10}=\cfrac{2}{5a}\implies 35a=20\implies a=\cfrac{20}{35}\implies a=\cfrac{4}{7}$