Chapter2.1

Evaluating Algebraic Expressions

2-1 Rational Numbers

Warm Up

California StandardsCalifornia Standards

Lesson Presentation

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Warm UpDivide.

12 24

34

16

1. 36 3 2. 144 6

3. 68 17 4. 345 115

5. 1024 64



California Standards

NS1.5 Know that every rational number is either a terminating or a repeating decimal and be able to convert terminating decimals into reduced fractions.NS1.3 Convert fractions to decimals and percents and use representations in estimations, computations, and applications.



rational numberterminating decimalrepeating decimal

Vocabulary



A rational number is any number that can be written as a fraction , where n

and d are integers and d 0.

nd

Any fraction can be written as a decimal by dividing the numerator by the denominator. If the division ends or terminates, because the remainder is zero, then the decimal is a terminating decimal.



If the division leads to a repeating block of one or more digits (where all digits are not zeros) after the decimal point, then the decimal is a repeating decimal. A repeating decimal can be written with a bar over the digits that repeat. So 0.13333… = 0.13.



9 11 The pattern repeats.

1

–9

.2

2

0

.0

2

11 9

–1 8

Additional Example 1A: Writing Fractions as Decimals

Write the fraction as a decimal.

The fraction is equivalent to the decimal 1.2.11 9



This is a terminating decimal.20 7

.30 5

The remainder is 0.

7 20

–07

1 0

0

0

0

.0

0–6 0

–1 0 0

Additional Example 1B: Writing Fractions as Decimals





9 15 The pattern repeats, so draw a bar over the 6 to indicate that this is a repeating decimal.

1

–9

.6

6

0

.0

6

15 9

–5 4


Check It Out! Example 1A




40 9 This is a terminating decimal.

.20 2

The remainder is 0.

9 40

–09

1 0

0

0

.0

0–8 0

– 8 02 0

0

0

5

0– 2 00

Write the fraction as a decimal.Check It Out! Example 1B




To write a terminating decimal as a fraction, identify the place value of the digit farthest to the right. Then write all of the digits after the decimal point as the numerator with the place value as the denominator.



5.37

A. 5.377 is in the hundredths place, so write hundredths as the denominator.

37 100

= 5

Additional Example 2: Writing Terminating Decimals as Fractions

Write each decimal as a fraction in simplest form.

0.622

B. 0.6222 is in the thousandths place, so write thousandths as the denominator.

622 1000

=

= 311 500

Simplify by dividing by the greatest common divisor.



A fraction is in reduced, or simplest, form when the numerator and the denominator have no common divisor other than 1.

Remember!



8.75

A. 8.75 5 is in the hundredths place, so write hundredths as the denominator.

75 100

= 8

= 8 3 4


Write each decimal as a fraction in simplest form.Check It Out! Example 2

0.2625

B. 0.26255 is in the ten-thousandths place.

2625 10,000

=

= 21 80




x = 0.44444… Let x represent the number.

Additional Example 3: Writing Repeating Decimals as Fractions

Write 0.4 as a fraction in simplest form.

10x = 10(0.44444…) Multiply both sides by 10 because 1 digit repeats.

Subtract x from both sides to eliminate the repeating part. Since x = 0.44444…, use 0.44444… for x on the right side of the equation.

_

10x = 4.444444…

x = 0.44444…

9x = 4

9x = 4 9 9

Since x is multiplied by 9, divide both sides by 9.

x = 4 9



x = 0.363636… Let x represent the number.

Check It Out! Example 3

Write 0.36 as a fraction in simplest form.

100x = 100(0.363636…) Multiply both sides by 100 because 2 digits repeat.

Subtract x from both sides to eliminate the repeating part. Since x = 0.363636…, use 0.363636… for x on the right side of the equation.

__

100x = 36.363636…

x = 0.363636…

99x = 36

99x = 36 99 99

Since x is multiplied by 99, divide both sides by 99.

x = =36 99

4 11

Write in simplest form.


2-1 Rational NumbersLesson Quiz

Write each decimal as a fraction in simplest form.

1. 0.27 2. –0.625

3. Write as a decimal. 2.16

27 100

– 5 8

13 6

Tommy had 13 hits in 40 at bats for his baseball team. What is his batting average? (Batting average is the number of hits divided by the number of at bats, expressed as a decimal.)

6.

0.325

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Chapter2.1