Question

I was charged $ 1.20 for sales tax when I spent $20. How much sales tax would I pay on a purchase of $50

Answer 1

well, keeping in mind that taxes are a percent of the price value, so we know that 1.20 is really some percent of 20, whilst 20 is the 100%, so what is 1.20 off of it in percentage?

$\bf \begin{array}{ccll} amount&\%\\ \cline{1-2} 20&100\\ 1.20&x \end{array}\implies \cfrac{20}{1.20}=\cfrac{100}{x}\implies 20x=120 \\\\\\ x=\cfrac{120}{20}\implies x=6\qquad \impliedby \textit{so then the tax applied is 6\%} \\\\[-0.35em] ~\dotfill\\\\ \begin{array}{|c|ll} \cline{1-1} \textit{a\% of b}\\ \cline{1-1} \\ \left( \cfrac{a}{100} \right)\cdot b \\\\ \cline{1-1} \end{array}~\hspace{5em}\stackrel{\textit{6\% of 50}}{\left( \cfrac{6}{100} \right)50}\implies 3$