 ## Presentation on theme: "Adding & Subtracting Decimals"— Presentation transcript:

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

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 Example: Fifty-hundredths . 5 Ones Tenths Hundredths
. 5 CONFIDENTIAL

Your Turn! Eight Hundredths Ones Tenths Hundredths CONFIDENTIAL

Place Value Example: Three hundred forty-four thousandths . 3 4 4
Ones Tenths Hundredths Thousandths . 3 4 4 0.344 CONFIDENTIAL

Your Turn Twenty-seven thousandths Ones Tenths Hundredths Thousandths
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Compare & Order Decimals
Use a number line Compare 5.7 and 5.9 5.7 is to the left of 5.9, 5.7 < 5.9 CONFIDENTIAL

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 Think: 5 = 5 Think: 7 < 9 5.7 < 5.9 CONFIDENTIAL

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

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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. Three and eighteen hundredths 3.18 CONFIDENTIAL

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

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

Rounding Round 5.3 to the nearest whole number
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 CONFIDENTIAL

Your Turn Round 5.6 to the nearest whole number
Round 5.6 to the nearest whole number Round 5.2 to the nearest whole number CONFIDENTIAL

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

Rounding Round 1.56 to the nearest tenth
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 CONFIDENTIAL

Your Turn Round 1.58 to the nearest tenth
Round 1.58 to the nearest tenth Round 1.52 to the nearest tenth CONFIDENTIAL

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: 1.85 CONFIDENTIAL

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 1.17 + 1.38 2.55 CONFIDENTIAL

Estimate Sums Use Rounding For Example: Estimate: 586.47 + 23.97
Step 1: Round each addend to the nearest whole number Step 2: Add For Example: Estimate: rounds to 586 23.97 rounds to 24 586 + 24 610 Think: 4 < 5 Round down Think: 9 > 5 Round up CONFIDENTIAL

Your Turn Estimate the sum by rounding to the nearest whole number CONFIDENTIAL

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

Subtracting Decimals Step 3:Write a decimal to show the total number of shaded squares that are not crossed out. 0.6 CONFIDENTIAL

Your Turn Find the difference; 0.9 – 0.2 CONFIDENTIAL

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 – 14.25 25.80 7 10 11.55 CONFIDENTIAL

Estimate Differences Use Rounding Example: Estimate 12.25 – 5.79
To estimate differences of decimals, round each decimal to the nearest whole number. Then subtract the rounded numbers. Example: Estimate – 5.79 12.25: Round down to 12 5.79: Round up to 6 Subtract: 12 – 6 = 6 So – 5.79 is about 6. CONFIDENTIAL

Your Turn Estimate. Round to the nearest whole number. 9.7 – 4.3
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Let us take a break! CONFIDENTIAL

Let us see how fast you are on this one!
Jig-Saw puzzle Let us see how fast you are on this one! Click me CONFIDENTIAL

Assessment Use place value chart to read and write decimals: 7/1,000
513/1,000 CONFIDENTIAL

Assessment Order from greatest to least: 3.2, 4.5, 3.9, 4.1
5.33, 4.91, 5.19, 5.52 CONFIDENTIAL

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

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

Assessment Round to the nearest tenth. 7.24
Round to the nearest hundredth. 8.236 CONFIDENTIAL