[tex]\bf 4:15~~=~~15:20\qquad \qquad \cfrac{4}{15}=\cfrac{15}{20}\implies \cfrac{2\cdot 2}{3\cdot 5}=\cfrac{3\cdot ~~\begin{matrix} 5 \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~}{2\cdot 2\cdot ~~\begin{matrix} 5 \\[-0.7em]\cline{1-1}\\[-5pt]\end{matrix}~~}\implies \cfrac{4}{15}\ne \cfrac{3}{4}~~\bigotimes[/tex]
