Calculate Percentage

Calculating percentages is a common, everyday task.  However, many people are easily confused when faced with this mathematical problem.  This is why, for example, they often over (or under) tip for the service they receive in a restaurant.

If you have ever struggled with how much to leave for a tip or what part of your paycheck goes to groceries or fuel, this article is for you. With a little practice and following the formula in this article, you will soon wonder why percentages ever seemed difficult.

How, then, does this apply to percentages? A percentage is simply a ratio solving for a certain hundredth. (Percent comes from the Latin phrase, per cent, “by the hundred.”) A simple problem will illustrate the process. What percentage of two is one? Or stated otherwise, how do you convert one-half into a percentage?

• Just set up the previous formula: ½ ∼ x/100.
• Multiply the extremes and then divide by the known mean.
• 1 x 100 = 100 $ 100 ÷ 2 = 50; and 50 is your answer.

Now it is time for a more challenging problem. Suppose you have just dined at a restaurant and have been presented with a bill for $37.95. You want to leave a 15 percent tip. Set up your formula and solve for x.

• x/37.95 ∼ 15/100. [x is to 37.95 as 15 is to 100].
• Multiply the means: 37.95 x 15 = 569.25.
• Divide the result (569.25) by 100, and you will have your answer: $5.69.

However daunting this calculation may seem, it is actually quite simple and goes back to the process of calculating a ratio. If someone asked you what three-fourths of twenty is, you would quickly respond with the correct answer: fifteen. But do you know the method you followed to arrive at the solution? It went something like this:

• You set up the following formula: 3/4 ∼ x/20. In laymen’s terms this reads, “Three is to four as x is to twenty.”
• Next, you multiplied the extremes (the outside numbers) and divided by the known mean (inside or middle number).
• Three times twenty equals sixty. Then, sixty divided by four equals fifteen, your solution.

You can follow the same process to compute the unknown in any part of this equation. In the above example, if you wanted to solve for one of the extremes, your equation might look like this: 3/4 ∼ 15/x. In this case, multiply the means (four and fifteen) and then divide by the known extreme (three). The result is twenty.

Are you ready to try one on your own? You know the formula, so just plug in the numbers. If your bill at the garage was $63.00 and you want to give the mechanic an 18 percent tip, how much do you owe him? Work it out for yourself before looking at the solution, given at the end of this article.

As you can see, calculating percentages is not very difficult. Just use the simple mathematic concepts of ratios and equivalency, and this process will soon be second nature. Of course, it is up to you whether you calculate your tip before or after taxes have been added to the bill. Did you get $11.34 for your answer? Congratulations!