CONFIDENTIAL 1

Today we will review the Chapter:

Adding & Subtracting Decimals

Good Afternoon!

Let’s Warm up:.

1) 3 + 4 x 7 = 2) (35 ÷ 5) - 7 =

3) 9 + 54 ÷ 6 = 4) 65 - 7 x 9 =

CONFIDENTIAL 2

Decimals

Decimal: A number that uses place value and a decimal point to show tenths, hundredths, and thousandths. 0.1 is a decimal number for one tenth. 0.12 is a decimal for twelve hundredths. 0.125 is a decimal for one hundred twenty-five thousandths.

Decimal point: A period separating the ones and the tenths in a decimal. 2.7

Equivalent Decimals: Decimals that name the same number. 0.3 and 0.30 are equivalent decimals.

CONFIDENTIAL 3

Place Value

Example: Fifty-hundredths

Ones Tenths Hundredths

0 . 5 0

CONFIDENTIAL 4

Your Turn!

Eight Hundredths

Ones Tenths Hundredths

CONFIDENTIAL 5

Place Value

Example: Three hundred forty-four thousandths

Ones Tenths Hundredths

0 . 3 4

Thousandths

4

0.344

CONFIDENTIAL 6

Your Turn

Twenty-seven thousandths

Ones Tenths Hundredths Thousandths

CONFIDENTIAL 7

Compare & Order Decimals

Use a number line Compare 5.7 and 5.9

5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.0

5.7 is to the left of 5.9, 5.7 < 5.9

CONFIDENTIAL 8

Compare & Order Decimals

Use place value Step 1

Line up the decimal points. Compare the ones.5.75.9

Step 2 Compare the tenths5.75.9

Think: 5 = 5

Think: 7 < 9

5.7 < 5.9

CONFIDENTIAL 9

Your Turn

Order 5.49, 5.4, 5.57, and 6.03 from greatest to least

CONFIDENTIAL 10

Decimals and fractions

Use models

This model shows 1

This model shows 1 divided into 10 equal parts. The shaded portion shows 1/10. It can be written as 0.1

This model shows 1 divided into 100 equal parts. The shaded portion shows 1/100. It can be written as 0.01

CONFIDENTIAL 11

Decimals and fractions

Use models Show twenty-five hundredths as a

decimal Use graph paper to model fractions

and decimals Count 10 rows of 10 squares each for

a total of 100 squares Color 25 squares in the 100 square

grid Write the fraction of the grid that is

shaded: 25/100 Place a zero and a decimal point in

front of the numerator of the fraction to make the decimal 25/100 = 0.25

CONFIDENTIAL 12

Your Turn

Write a fraction and decimal for the shaded part.

CONFIDENTIAL 13

Decimals and Mixed Numbers

Decimals greater than 1 A mixed number is made up of a whole and a part of a

whole Example: Write as a decimal. 100

183

Three and eighteen hundredths3.18

CONFIDENTIAL 14

Your Turn

Write a mixed number and a decimal to tell how much is shaded.

CONFIDENTIAL 15

Rounding

Use a number line to round decimals To round a decimal to the nearest whole number, look

at the digit in the tenths place. If the tenths digit is 5 or greater, round up to the

nearest one. If the tenths digit is less than 5, round down to the

nearest one.

CONFIDENTIAL 16

Rounding

Round 5.3 to the nearest whole number Think: 5.3 is closer to 5 than 6 So, 5.3 rounds down to 5

Round 5.8 to the nearest whole number Think: 5.8 is closer to 6 than 5 So, 5.8 rounds up to 6

5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.0

CONFIDENTIAL 17

Your Turn

Round 5.6 to the nearest whole number

Round 5.2 to the nearest whole number

5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.0

CONFIDENTIAL 18

Rounding

To round to the nearest tenth, look at the digit in the hundredths place. If the hundredths digit is 5 or greater, round up to the

nearest tenth. If the hundredths digit is less than 5, round down to

the nearest tenth.

CONFIDENTIAL 19

Rounding

Round 1.56 to the nearest tenth Think: 1.56 is closer to 1.60 than 1.50 So, 1.56 rounds up to 1.60

Round 1.51 to the nearest tenth Think: 1.51 is closer to 1.50 than 1.60 So, 1.51 rounds down to 1.50

1.50 1.51 1.52 1.53 1.54 1.55 1.56 1.57 1.58 1.59 1.60

CONFIDENTIAL 20

Your Turn

Round 1.58 to the nearest tenth

Round 1.52 to the nearest tenth

1.50 1.51 1.52 1.53 1.54 1.55 1.56 1.57 1.58 1.59 1.60

CONFIDENTIAL 21

Adding Decimals

Use models to add decimals Step 1: Draw two 10 by 10

grids on graph paper Show 1.5 by coloring one

whole grid red and coloring 50/100 of the second grid red.

Step 2: Show 0.35 by coloring 35/100 of the second grid blue.

Step 3:Count the shaded squares in each grid. Write this in decimal form.

Find: 1.5 + 0.35

1.85

CONFIDENTIAL 22

Your Turn

Find 3.38 + 0.34

CONFIDENTIAL 23

Adding Decimals

Step 1: Line up the decimal points Step 2: Add each place. Regroup if needed.

Write the decimal point in the sum. Example: Find 1.17 + 1.38

1

1.17+ 1.38

2.55

CONFIDENTIAL 24

Your Turn

Add 0.36 + 0.46

CONFIDENTIAL 25

Estimate Sums

Use Rounding Step 1: Round each

addend to the nearest whole number

Step 2: Add

For Example: Estimate: 586.47 + 23.97 586.47 rounds to 586 23.97 rounds to 24

586

+ 24610

Think: 4 < 5 Round

down

Think: 9 > 5 Round

up

CONFIDENTIAL 26

Your Turn

Estimate the sum by rounding to the nearest whole number. 5.7 + 4.1

CONFIDENTIAL 27

Subtracting Decimals

Use models Example: Find 2.5 – 1.9

Step 1:Draw three 10 by 10 grids; show 2.5 by coloring 2 whole grids and 50 small squares red.

CONFIDENTIAL 28

Subtracting Decimals Step 2:Cross out 1 whole grid and 90 small squares to show

subtracting 1.9

CONFIDENTIAL 29

Subtracting Decimals Step 3:Write a decimal to show the total number of shaded

squares that are not crossed out.0.6

CONFIDENTIAL 30

Your Turn

Find the difference; 0.9 – 0.2

CONFIDENTIAL 31

Subtracting Decimals

Step 1:Line up the decimal points. Insert a zero if needed.

Step 2:Subtract each place. Regroup if needed. Write the decimal point.

Step 3: You can use the inverse relationship between addition and subtraction to check.

Example: 25.8 – 14.2525.80

- 14.25

7 10

25.80- 14.25

11.55

11.55+ 14.25

25.80

CONFIDENTIAL 32

Your Turn

Subtract. Check the answer. 0.96 – 0.29

CONFIDENTIAL 33

Estimate Differences

Use Rounding To estimate differences of decimals, round each

decimal to the nearest whole number. Then subtract the rounded numbers.

Example: Estimate 12.25 – 5.79 12.25: Round down to 12 5.79: Round up to 6 Subtract: 12 – 6 = 6

So 12.25 – 5.79 is about 6.

CONFIDENTIAL 34

Your Turn

Estimate. Round to the nearest whole number. 9.7 – 4.3

CONFIDENTIAL 35

Let us take a break!

CONFIDENTIAL 36

Jig-Saw puzzle

Click me

Let us see how fast you are on this one!

CONFIDENTIAL 37

Assessment

Use place value chart to read and write decimals:1. 7/1,000

2. 513/1,000

CONFIDENTIAL 38

Assessment

Order from greatest to least:1. 3.2, 4.5, 3.9, 4.1

2. 5.33, 4.91, 5.19, 5.52

CONFIDENTIAL 39

Assessment

1. Write a mixed number and a decimal to tell how much is shaded.

CONFIDENTIAL 40

Assessment

2. Write a mixed number and a decimal to tell how much is shaded.

CONFIDENTIAL 41

Assessment

Round to the nearest tenth.1. 7.24

Round to the nearest hundredth.2. 8.236

CONFIDENTIAL 42

Assessment

1. Add4.7185.2

+ 3.989

2. Add. Estimate to check for reasonableness.19.76 + 9.55

CONFIDENTIAL 43

Assessment

1. Subtract. Check answer.1.54

- 0.39

2. Subtract. Estimate to check for reasonableness.7.1 – 2.70

CONFIDENTIAL 44

Good Job!

You have learned a lot today!!!