Question

the sales tax for an item was $7.80 and it cost $390 before tax. find the sales tax rate. write your answer as a percentage.

Answer 1

$390 represent 100%. To find what percentage $7.80 represent, we can use the next proportion:

$\frac{390\text{ \ }}{7\text{.8 \ }}=\frac{100\text{ \%}}{x\text{ \%}}$

Solving for x,

$\begin{gathered} 390\cdot x=100\cdot7.8 \\ x=\frac{780}{390} \\ x=2\text{ \%} \end{gathered}$

The sales tax rate is 2%