Monica paid sales tax of $3.20 when she bought a new bike helmet. If the sales tax rate was 8%, how much did the store charge for the bike helmet before tax?

Answer: the store charged $40 for the bike helmet before tax.

Step-by-step explanation:

Let x represent the amount that the store charge for the bike helmet before tax.

If the sales tax rate was 8%, it means that the amount of tax that was charge is

8/100 * x = 0.08 * x = 0.08x

Monica paid sales tax of $3.20 when she bought a new bike helmet. This means that

0.08x = 3.2

Dividing the left hand side and the right hand side of the equation by 0.08, it becomes

0.08x/0.08 = 3.2/0.08

x = 40