Question

sales tax is calculated
before a sale discount is applied.
based on the number of items purchased.
using a percentage of the price of an item.
as a percentage based on federal law applied.

Explanation:

To determine how sales tax is calculated, we analyze each option:

Step1: Analyze "as a percentage based on federal law"

Sales tax rates are set by state/local, not federal law (except some special cases, but generally state/local). So this is incorrect.

Step2: Analyze "using a percentage of the price of an item"

Sales tax is typically a percentage (e.g., 6%) of the item's price. This matches the standard calculation: \( \text{Sales Tax} = \text{Item Price} \times \text{Tax Rate (Percentage)} \).

Step3: Analyze "based on the number of items purchased"

Sales tax is not based on quantity of items, but on their total price. So this is incorrect.

Step4: Analyze "before a sale discount is applied"

Sales tax is calculated on the price after discounts in most cases (depends on jurisdiction, but the main calculation is based on the item's price, not discount timing for the core formula). But the key correct description is the percentage of the item's price.

Answer:

using a percentage of the price of an item