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One of the most important steps in calculating sales tax involves converting a percentage to its decimal form. This process is fundamental because percentages themselves are not used directly in calculations. To convert a percentage to a decimal, you simply divide the percentage by 100. For example, a percentage of 714% becomes a decimal of 7.14 by dividing 714 by 100.

Understanding why we divide by 100 can be helpful. The term "percent" comes from the Latin phrase "per centum," meaning "by the hundred." Thus, a percentage is essentially a fraction out of 100. When we say 50%, we mean 50 out of 100, or 0.5 when expressed as a decimal. This conversion is crucial to appropriately utilize the percentage in mathematical computations, like finding sales tax or discounts.

After converting the percentage to a decimal, the next step is multiplying it with the item's cost to ascertain the sales tax amount. Multiplying decimals can initially seem tricky, but it's quite straightforward once you understand the process.

Here’s how to multiply decimals:

• First, ignore the decimal points and multiply the numbers as if they were whole numbers.
• Next, count the total number of decimal places in both numbers. For example, if one number has two decimal places and the other has one, the total decimal places will be three.
• Then, place the decimal point in the result, ensuring it has the same total number of decimal places you counted earlier.

For instance, multiplying 129.99 by 7.14 works this way. It’s as if you are multiplying 12999 by 714, and then adjusting the decimal point to account for the four decimal places combined in the original figures, which gives us the sales tax amount.

To find the total cost after tax, you need to sum the original price of the item with the calculated sales tax. This final addition gives you the total amount that you would actually pay.

In practice, this means:

• First, identify the original cost, like the initial $129.99 in this example.
• Second, add the sales tax amount, which we calculated earlier as $928.89.
• Finally, add these two amounts together: $129.99 + $928.89 = $1058.88.

Through this process, you derive the total cost including sales tax, ensuring you are aware of the full price necessary for purchasing the item, which is essential for budgeting and financial planning.