Algebra I: 1001 Practice Problems For Dummies (+ Free Online Practice)
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You can simplify decimals and fractions by rounding off. To round off a decimal number, you limit the number of decimal places that the number holds. To round off a fraction, you first convert the fraction to a decimal. If the division ends in a repeating decimal, you can stop after a certain number of decimal places and round off.

Rounding numbers results in an estimated or approximate value.

To round numbers:

  1. Determine the number of places you want, and go one further.

  2. Increase the last place you want by one number if the one further is 5 or greater.

  3. Leave the last place you want as is, if the one further is less than 5.

Here are some examples of fractions that need to be rounded:

Example 1: The fraction 5/9 won't divide evenly — it ends in a repeating decimal.

Change 5/9 to a decimal by dividing 5 by 9.

5 ÷ 9 = .5555…

If you choose to round to three decimal places, look one digit beyond the third decimal place, which is 5.

If the digit is 5 or greater, then you round up.

So .5555… ≈ .556

The symbol ≈ means approximately the same or about equal. This is a useful symbol for when you are rounding a number.

Example 2: The fraction 4/7 won't divide evenly — it’s another repeating decimal that'll go on forever when divided.

Change 4/7 to a decimal by dividing 4 by 7.

4 ÷ 7 = .57142857142857…

If you choose to round to 4 decimal places, look at the first digit beyond the fourth decimal place, which is 2.

If the digit is less than 5, then you don't round up.

So .57142… ≈ .5714

About This Article

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About the book author:

Mary Jane Sterling taught algebra, business calculus, geometry, and finite mathematics at Bradley University in Peoria, Illinois, for more than 30 years. She is the author of several For Dummies books, including Algebra Workbook For Dummies, Algebra II For Dummies, and Algebra II Workbook For Dummies.

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