1. 7 Chapter Decimals: Rational Numbers and Percent
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2. NCTM Standard: Decimals and Real Numbers
Students in grades 6−8 should
work flexibly with fractions, decimals, and percents to solve problems;
compare and order fractions, decimals, and percents efficiently and find their approximate locations on a number line;
develop an understanding of large numbers and recognize and appropriately use exponential, scientific, and calculator notation;
understand the meaning and effects of arithmetic operations with fractions, decimals, and integers. (p. 214)
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3. 7-3 Nonterminating Decimals
Repeating Decimals
Writing a Repeating Decimal in the Form a/b,
A Surprising Result
Ordering Repeating Decimals
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Repeating Decimals
We have examined decimal numbers such as 0.475, which stop, and are called terminating decimals. Not all rational numbers can be represented by terminating decimals.
For example, converting 2/11 into a decimal using the long division process indicates that we will actually get …, with the digits 18 repeating over and over indefinitely.
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Repeating Decimals
A decimal of this type is a repeating decimal, and the repeating block of digits is the repetend.
The repeating decimal is written 0.18, where the bar indicates that the block of digits underneath is repeated continuously.
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Example 7-10
Convert the following to decimals:
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7. Writing a Repeating Decimal in the Form
Write 0.5 as a rational number in the form
Step 1: Let x = 0.5, so that x = …
Step 2: Multiply both sides of the equation x = … by 10. (Use 10 since there is one digit that repeats.)
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8. Writing a Repeating Decimal in the Form
Step 3: Subtract the expression in step 1 from the final expression in step 2.
Step 4: Solve the equation 9x = 5 for x.
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9. Writing a Repeating Decimal in the Form
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10. Writing a Repeating Decimal in the Form
In general, if the repetend is immediately to the right of the decimal point, first multiply by 10m where m is the number of digits in the repetend, and then continue as in the preceding cases.
Suppose the repeating block does not occur immediately after the decimal point. A strategy for solving this problem is to change it to a related problem we know how to solve; that is, change it to a problem where the repeating block immediately follows the decimal point.
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11. Writing a Repeating Decimal in the Form
Write as a rational number in the form
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A Surprising Result
Write 0.9 as a rational number in the form
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13. Ordering Repeating Decimals
Order repeating decimals in the same manner as for terminating decimals.
Compare with
Line up the decimals, then starting at the left, find the first place where the face values are different.
Since 3 > 2, >
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Example 7-12
Find a rational number in decimal form between 0.35 and
Starting from the left, the first place at which the two numbers differ is the thousandths place.
One decimal between these two is
Others include , , and
There are infinitely many others.
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