Monica paid sales tax of $1.80 when she bought a new bike helmet. If the sales tax rate was 9%, how much did the store charge for the bike helmet before tax?

Let the charge of helmet befor tax be x

so
9% of x= 1.80

9x/100 = 1.80

x =(1.80*100)/9

= 20

0.09x = 1.80

Solve for x.

To find out how much the store charged for the bike helmet before tax, we can use the formula:

Original price = Price + Sales tax

We know that the sales tax paid by Monica was $1.80, and the sales tax rate was 9%. Let's assign a variable to the original price, say "x". So, we can write the equation as:

x = x + 0.09x

Simplifying the equation:

x = 1.09x

To solve for "x", we can divide both sides of the equation by 1.09:

x / 1.09 = 1.09x / 1.09

This simplifies to:

x ≈ 1.80 / 0.09

Performing the calculation:

x ≈ 20

Therefore, the store charged Monica $20 for the bike helmet before tax.

To find the cost of the bike helmet before tax, we need to divide the sales tax amount by the tax rate.

First, let's represent the cost of the bike helmet before tax as 'x'.

We know that the sales tax is 9% or 0.09 in decimal form.

We also know that Monica paid sales tax of $1.80.

So, we can set up the equation:

0.09 * x = $1.80

To solve for 'x', we divide both sides of the equation by 0.09:

x = $1.80 / 0.09

Now we can calculate:

x = $20

Therefore, the store charged Monica $20 for the bike helmet before tax.