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Repeating Decimals

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Repeating Decimals

Have you ever eaten a part of a pie and you couldn't figure out how much you ate?

While Daniel ate peach pie, Natalia ate blueberry. Her pie was cut into nine pieces and she ate only two of them.

What fraction of the pie did she eat? What is this fraction as a decimal?

In this Concept, you will learn about repeating decimals. Then you will see how this applies to Natalia.

Guidance

By now you’ve gotten the hang of converting fractions to decimals. So far, we have been working with what are known as terminating decimals , or decimals that have an end like 0.75 or 0.5.

One reason that we sometimes use fractions instead of decimals is because some decimals are repeating decimals , or decimals that go on forever. If you try to find a decimal for \frac{1}{3} by dividing, you can divide forever because \frac{1}{3} written as a decimal = 0.3333333333 .... It goes on and on. That’s why we usually just simply write a line above the number that repeats. For \frac{1}{3} , we write: 0.\overline{3} . Let’s check out some problems involving repeating decimals.

Write \frac{5}{6} using decimals

First, we rewrite \frac{5}{6} as the division problem 5 \div 6 . We already know that we will have to go on the right side of the decimal point, so we are going to begin by dividing 6 into 5.0.

Six goes into 5.0 .8 times, but we have the remainder of .2. Six goes into 0.2 .03 times and we have a remainder of .02. Since 6 always goes into 20 three times, (3 \cdot 6 = 18) and there will always be a remainder of 2, we can see that it will never evenly divide.

If you keep dividing, you will get 0.83333333333.... forever and ever.

Our final answer is 0.8\overline{3} .

What about mixed numbers?

Well, there are some mixed numbers where the fraction part is a repeating decimal. Let’s look at one like this.

Write 2 \frac{2}{3} using decimals.

Just as we did with the terminating decimals, we are going to leave the whole number, 2 to the side before we are ready to add it to the final answer. So, we are simply solving for the decimal equivalent of \frac{2}{3} . We write the division problem 2.0 \div 3 . How many times does 3 go into 2.0? It goes into 2.0 0.6 times.

We have 0.20 as the remainder. How many times does 3 go into 0.20? The answer is 0.06 times.

Are you noticing a pattern here? It is obvious that there will always be a remainder whether we divide 3 into 2.0, 0.2, 0.02, 0.002, or 0.0002 and on and on. Clearly \frac{2}{3} is a repeating decimal.

For our final answer we write 2.\overline{6} .

Try a few of these on your own. Convert each to a repeating decimal.

Example A

\frac{1}{6}

Solution: .1\overline{6}

Example B

4 \frac{4}{6}

Solution: 4.\overline{6}

Example C

\frac{4}{9}

Solution: .\overline{4}

Here is the original problem once again.

While Daniel ate peach pie, Natalia ate blueberry. Her pie was cut into nine pieces and she ate only two of them.

What fraction of the pie did she eat? What is this fraction as a decimal?

First, let's write the fraction of two out of nine.

\frac{2}{9}

Now let's divide the numerator by the denominator.

.222222222

We have repeating decimal. We can rewrite this repeating decimal using different notation as it was presented in the Concept.

.\overline{2}

This is our answer.

Vocabulary

Fraction
a part of a whole written using a numerator and a denominator and a fraction bar
Decimal
a part of a whole written using a decimal point and place value
Mixed Number
a number written with a whole number and a fraction.
Terminating Decimal
a decimal with an ending.
Repeating Decimal
a decimal that does not end but repeats and repeats

Guided Practice

Here is one for you to try on your own.

Write 2 \frac{1}{6} as a decimal.

Answer

To do this, first, we have to convert the mixed number to an improper fraction.

\frac{13}{6}

Now we divide the numerator by the denominator.

2.1666666

We have a repeating decimal. We can rewrite this using decimal notation.

2.1\overline6

This is our answer.

Video Review

This is a James Sousa video on writing fractions as repeating decimals.

Practice

Directions: Write each fraction or mixed number as a repeating decimal or terminating decimal.

1. \frac{2}{3}

2. \frac{5}{6}

3. 5 \frac{1}{3}

4. \frac{1}{3}

5. \frac{3}{4}

6. \frac{1}{6}

7. \frac{1}{8}

8. \frac{3}{7}

9. \frac{2}{6}

10. 4 \frac{2}{3}

11. 7 \frac{1}{3}

12. 6 \frac{5}{6}

13. 8 \frac{1}{2}

14. 9 \frac{2}{3}

15. 11 \frac{1}{5}

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