Question

the sales tax for an item was $21.70 and it cost $310 before tax. find the sales tax. write your answer as a percentage

Answer 1

so we know the cost was $310 and a tax on it of say "t" percent, ended up as $21.70.

So if we take 310 as the 100%, what's "t"?

`\begin{array}{ccll} Amount&\%\\ \cline{1-2} 310 & 100\\ 21.70& t \end{array} \implies \cfrac{310}{21.70}~~=~~\cfrac{100}{t}\implies 310t=2170 \\\\\\ t=\cfrac{2170}{310}\implies t=7`