Praxis Core Prep: How to Convert between Decimals and Percents - dummies

Praxis Core Prep: How to Convert between Decimals and Percents

By Carla Kirkland, Chan Cleveland

You will be faced with decimals and percents on the Praxis Core. A percent is nothing more than another way to express a fraction. For example, 100% means 100 hundredths, or 100/100, which is 1. To convert a percent to a fraction, drop the percent sign and put the number over 100. Don’t forget to simplify.

5% = 5/100 = 1/20

A fraction represents division. The numerator is divided by the denominator.

A decimal has an integer followed by a decimal point and at least one digit after the decimal point. Because the second place after the decimal point is the hundredths place, dividing a decimal number by 100 is the same as moving its decimal point two places to the left. Moving a decimal point two places to the left results in a number that is 1/100 of the original number.

275.34% = 275.34 ÷ 100 = 2.7534

That’s why changing a percent to a decimal number involves just dropping the percent sign and moving the decimal two places to the left. For example, 73% (which is 73.0 percent) is equal to 0.73.

To go in the other direction, do the reverse. Converting a decimal into a percent involves moving the decimal two places to the right and adding a percent sign. That’s because multiplying by 100 and dividing by 100 undo each other. It’s like taking a step forward and taking a step back.

0.589 = 0.589 × 100 = 58.9%

Every time you move a decimal point one place to the left, you divide by 10. Every time you move a decimal one place to the right, you multiply by 10.

In order to change a fraction to a decimal, divide the numerator by the denominator with your calculator.

3/8 = 0.375

To convert a fraction to a percent, divide the numerator by the denominator to write the fraction in decimal form. Then convert the decimal form to a percent by multiplying by 100.

3/8 = 0.375 = 0.375 × 100 = 37.5%

Which of the following percents is equal to the fraction 3/5?

  • (A) 60%

  • (B) 30%

  • (C) 35%

  • (D) 65%

  • (E) 3/5%

The correct answer is Choice (A). By dividing 3 by 5, you get 0.6. If you move the decimal two places to the right and add a percent sign, you get 60%. Choices (B), (C), and (D) involve miscalculations, and Choice (E) results from the false method of simply adding a percent symbol.