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Today we will review the Chapter: Adding & Subtracting Decimals PowerPoint PPT Presentation


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Good Afternoon!. Today we will review the Chapter: Adding & Subtracting Decimals. Let’s Warm up:. 1) 3 + 4 x 7 = 31. 2) (35 ÷ 5) - 7 = 0. 3) 9 + 54 ÷ 6 = 18. 4) 65 - 7 x 9 = 2. Decimals.

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Today we will review the Chapter: Adding & Subtracting Decimals

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Today we will review the chapter adding subtracting decimals

Good Afternoon!

Today we will review the Chapter:

Adding & Subtracting Decimals

Let’s Warm up:.

1) 3 + 4 x 7 = 31

2) (35 ÷ 5) - 7 = 0

3) 9 + 54 ÷ 6 = 18

4) 65 - 7 x 9 = 2

CONFIDENTIAL


Decimals

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


Place value

Place Value

  • Example:

    • Fifty-hundredths

Hundredths

Ones

Tenths

0

.

5

0

CONFIDENTIAL


Your turn

Your Turn!

  • Eight Hundredths

Hundredths

Ones

Tenths

0

.

8

0

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Place value1

Place Value

  • Example:

    • Three hundred forty-four thousandths

Hundredths

Ones

Tenths

Thousandths

0

.

3

4

4

0.344

CONFIDENTIAL


Your turn1

Your Turn

  • Twenty-seven thousandths

Hundredths

Ones

Tenths

Thousandths

.

0

2

0

7

CONFIDENTIAL


Compare order decimals

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


Compare order decimals1

Compare & Order Decimals

  • Use place value

    • Step 1

      • Line up the decimal points. Compare the ones.

        5.7

        5.9

    • Step 2

      • Compare the tenths

        5.7

        5.9

Think: 5 = 5

Think: 7 < 9

5.7 < 5.9

CONFIDENTIAL


Your turn2

Your Turn

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

  • 6.03, 5.57, 5.49, 5.4

CONFIDENTIAL


Decimals and fractions

Decimals and fractions

  • Use models

This model shows 1

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

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

CONFIDENTIAL


Decimals and fractions1

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


Your turn3

Your Turn

  • Write a fraction and decimal for the shaded part.

  • 77/100; 0.77

CONFIDENTIAL


Decimals and mixed numbers

Decimals and Mixed Numbers

  • Decimals greater than 1

  • A mixed number is made up of a whole and a part of a whole

    • Example: Writeas a decimal.

Three and eighteen hundredths

3.18

CONFIDENTIAL


Your turn4

Your Turn

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

2.3

CONFIDENTIAL


Rounding

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


Rounding1

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


Your turn5

Your Turn

  • Round 5.6 to the nearest whole number

    • 6

  • Round 5.2 to the nearest whole number

    • 5

5.0 5.1 5.2 5.3 5.4 5.5 5.6 5.7 5.8 5.9 6.0

CONFIDENTIAL


Rounding2

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


Rounding3

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


Your turn6

Your Turn

  • Round 1.58 to the nearest tenth

    • 1.6

  • Round 1.52 to the nearest tenth

    • 1.5

1.50 1.51 1.52 1.53 1.54 1.55 1.56 1.57 1.58 1.59 1.60

CONFIDENTIAL


Adding decimals

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


Your turn7

Your Turn

  • Find 3.38 + 0.34 = 3.72

CONFIDENTIAL


Adding decimals1

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


Your turn8

Your Turn

  • Add 0.36 + 0.46 = 0.82

CONFIDENTIAL


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

+ 24

610

Estimate Sums

Think: 4 < 5 Round down

Think: 9 > 5 Round up

CONFIDENTIAL


Your turn9

Your Turn

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

    • 6 + 4 = 10

CONFIDENTIAL


Subtracting decimals

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


Subtracting decimals1

Subtracting Decimals

  • Step 2:Cross out 1 whole grid and 90 small squares to show subtracting 1.9

CONFIDENTIAL


Subtracting decimals2

Subtracting Decimals

  • Step 3:Write a decimal to show the total number of shaded squares that are not crossed out.

    0.6

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Your turn10

Your Turn

  • Find the difference; 0.9 – 0.2

    • 0.7

CONFIDENTIAL


Subtracting decimals3

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 – 14.25

25.80

- 14.25

7 10

25.80

-14.25

11.55

11.55

+14.25

25.80

Subtracting Decimals

CONFIDENTIAL


Your turn11

Your Turn

  • Subtract. Check the answer.

    • 0.96 – 0.29 = 0.67

    • Check: 0.29 + 0.67 = 0.96

CONFIDENTIAL


Estimate differences

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


Your turn12

Your Turn

  • Estimate. Round to the nearest whole number.

    • 9.7 – 4.3 = 10 – 4 = 6

CONFIDENTIAL


Let us take a break

Let us take a break!

CONFIDENTIAL


Jig saw puzzle

Jig-Saw puzzle

Let us see how fast you are on this one!

  • Click me

CONFIDENTIAL


Assessment

Assessment

Use place value chart to read and write decimals:

  • 7/1,000 = seven thousandths = 0.007

  • 513/1,000=five hundred thirteen thousandths = 0.513

Hundredths

Ones

Tenths

Thousandths

.

0

0

0

7

Hundredths

Ones

Tenths

Thousandths

.

5

1

0

3

CONFIDENTIAL


Assessment1

Assessment

Order from greatest to least:

  • 3.2, 4.5, 3.9, 4.1

    • 4.5, 4.1, 3.9, 3.2

  • 5.33, 4.91, 5.19, 5.52

    • 5.52, 5.33, 5.19, 4.91

CONFIDENTIAL


Assessment2

Assessment

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

1.67

CONFIDENTIAL


Assessment3

Assessment

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

2.55

CONFIDENTIAL


Assessment4

Assessment

Round to the nearest tenth.

  • 7.24 = 7.2

    Round to the nearest hundredth.

  • 8.236 = 8.24

CONFIDENTIAL


Assessment5

Assessment

  • Add

    4.718

    5.200

    +3.989

    13.907

  • Add. Estimate to check for reasonableness.

    19.76 + 9.55 = 29.31

    Estimate: 20 + 10 = 30

CONFIDENTIAL


Assessment6

Assessment

  • Subtract. Check answer.

    1.54

    -0.39

    1.15

    Chcek: 1.15 + 0.39 = 1.54

  • Subtract. Estimate to check for reasonableness.

    7.1 – 2.70 = 7.10 – 2.70 = 4.40

    Estimate: 7 – 3 = 4

CONFIDENTIAL


Good job

Good Job!

  • You have learned a lot today!!!

CONFIDENTIAL


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