Calculating Percentages

Calculating percent problems

There are many times in real life when you may need to calculate a percentage. You might need to figure out how much money a 5% discount will save you, or how much interest you'll pay on a loan with a 6% interest rate. Knowing how to calculate percentages will help you in both of these situations.

Setting up the calculation

Let's say the mailing department was responsible for 25% of the accidents at your company this year. There were 80 accidents total, and 20 of them were in the mailing department. You could write that like this:

25% of 80 = 20

This expression tells you that 25% of 80 is equal to 20. But what if you don't know how much a percentage is equal to? Let's say the demolition department was responsible for 50% of the 80 accidents. You don't know how many accidents 50% of 80 is. So you could write that like this:

50% of 80 = ?

To figure out what 50% of 80 is, you'll need to rewrite this example so it can be solved with math.

Click through the slideshow to see how to set up the example as a mathematical expression.

Finding how much a percent is worth

Let's imagine you scored 85% on your driving test. There were 20 questions on the test, and you want to figure out how many of them you got right. You just learned how to set up this example—now you'll learn how to solve it.

Click through the slideshow to learn how to find how much a percent is worth.

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Use decimals to calculate how much these percentages are worth.

You have a coupon for 20% off the price of a book. If the book you want usually costs $10, how much is the coupon worth?

There are 200 families in your town. The newspaper reports that 47% of them have more than two children. How many families in town have more than two children?

Your doctor saw 170 new patients last year. 60% of new patients were women. How many new female patients did your doctor see last year?

Finding the total

Over the past week, 40% of the phone calls to Alicia's cell phone were from her son. Let's say you know that her son called her 12 times. Now you want to find out how many total calls she received. We can rewrite this example like this:

40% of ? = 12

This time we're missing the total—we don't know how many calls Alicia received.

Click through the slideshow to see how to find the total.

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Find the missing whole in each of these problems.

Four students are sharing an apartment. Each pays 25% of the rent. If each student pays $200 per month, how much is the total rent for each month?

Jill has a 25% off coupon for some computer software. If the coupon saved her $35, how much would the software cost without the coupon?

Allen paid $12 in interest on his credit card this month. If you know that the interest rate on his card is 6%, how much was the total amount on his card?

Finding the percent

You just learned that 16 of your 32 cousins prefer chocolate ice cream to strawberry ice cream. You want to find out what percentage of your cousins likes chocolate ice cream. You can rewrite this example like this:

?% of 32 = 16

This time, the number we're missing is the percent. We want to know what percent is equal to 16 out of 32.

Click through the slideshow to learn how to find the percent.

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Find the percent in each of these examples.

30 out of 50 of the stores in your neighborhood sell pickles. What percentage of the stores sell pickles?

There are 200 elderly people in your neighborhood. 80 of them don't know how to send text messages. What percentage of elderly people in your neighborhood don't know how to send texts?

Your local team has won 9 out of 45 basketball games in the past year. What percentage of games did the team win?


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