Trigonometry Workbook For Dummies
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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

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