Question

How can you do this?

Answer 1

Check the picture below.

`\begin{array}{ccll} Amount&\%\\ \cline{1-2} 15 & 100\\ 3& x \end{array} \implies \cfrac{15}{3}~~=~~\cfrac{100}{x} \\\\\\ 5 ~~=~~ \cfrac{100}{x}\implies 5x=100\implies x=\cfrac{100}{5}\implies x=\stackrel{ \% }{20} \\\\[-0.35em] ~\dotfill`

`\begin{array}{ccll} Amount&\%\\ \cline{1-2} 15 & 100\\ 6& y \end{array} \implies \cfrac{15}{6}~~=~~\cfrac{100}{y} \\\\\\ \cfrac{5}{2} ~~=~~ \cfrac{100}{y}\implies 5y=200\implies y=\cfrac{200}{5}\implies y=\stackrel{ \% }{40}`