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3-3 Adding and Subtracting Decimals Course 1 Warm Up Warm Up Lesson Presentation Lesson Presentation Problem of the Day Problem of the Day

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Warm Up Estimate by rounding to the indicated place value. 1. 70.27 + 15.36; ones 2. 84.37 – 21.82; tenths Estimate each product or quotient. 3. 27.25 8.7 4. 44.52 ÷ 3.27 85 62.6 270 Course 1 3-3 Adding and Subtracting Decimals 15

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Problem of the Day Find a three-digit number that rounds to 440 and includes a digit that is the quotient of 24 and 3. Is there more than one possible answer? Explain your thinking. 438; no; the numbers that round to 440 are 435-444, 24 divided by 3 is 8, and 438 is the only number with 8 as a digit. Course 1 3-3 Adding and Subtracting Decimals

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Learn to add and subtract decimals. Course 1 3-3 Adding and Subtracting Decimals

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Course 1 3-3 Adding and Subtracting Decimals Estimating before you add or subtract will help you check whether your answer is reasonable. Helpful Hint

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Course 1 3-3 Adding and Subtracting Decimals Elise Ray’s Scores EventPoints Floor exercise9.8 Balance beam9.7 Vault9.425 Uneven bars9.85 American gymnast Elise Ray won the 2000 U.S. Championships in the all-around, uneven bars, and floor-exercise events. To find the total number of points, you add all of the scores.

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Course 1 3-3 Adding and Subtracting Decimals Additional Example 1A: Sports Application A. What was Elise Ray’s total for the events other than the floor exercise? Estimate by rounding to the nearest whole number. 9.7 + 9.425 + 9.85 The total is about 29 points. 10 + 9 + 10 = 29 Find the sum of 9.7, 9.425, and 9.85.

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Course 1 3-3 Adding and Subtracting Decimals Additional Example 1A Continued Add. 9.700 9.425 +9.850 28.975 Align the decimal points.Use zeros as placeholders.Add. Then place the decimal point. Since 28.975 is close to the estimate of 29, the answer is reasonable. Elise Ray’s total for the events other than the floor exercise was 28.975.

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Course 1 3-3 Adding and Subtracting Decimals Additional Example 1B: Sports Application B. How many more points did Elise need on the vault to have a perfect score of 10? 10.000 -9.425 0.575 Align the decimal points.Use zeros as placeholders.Subtract. Then place the decimal point. Elise needed another 0.575 points to have a perfect score. Find the difference between 10 and 9.425.

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Course 1 3-3 Adding and Subtracting Decimals Try This: Example 1A A. What was Elise Ray’s total for the events other than the vault exercise? Estimate by rounding to the nearest whole number. 9.8 + 9.7 + 9.85 The total is about 30 points. 10 + 10 + 10 = 30 Find the sum of 9.8, 9.7, and 9.85.

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Course 1 3-3 Adding and Subtracting Decimals Try This: Example 1A Continued Add 9.800 9.700 +9.850 29.350 Align the decimal points.Use zeros as placeholders.Add. Then place the decimal point. Since 29.350 is close to the estimate of 30, the answer is reasonable. Elise Ray’s total for the events other than the vault exercise was 29.350.

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Course 1 3-3 Adding and Subtracting Decimals Try This: Example 1B B. How many more points did Elise need on the uneven bars to have a perfect score of 1 10.00 -9.85 0.15 Align the decimal points.Use zeros as placeholders.Subtract. Then place the decimal point. Elise needed another 0.15 points to have a perfect score. Find the difference between 10 and 9.85.

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Course 1 3-3 Adding and Subtracting Decimals Additional Example 2: Using Mental Math to Add and Subtract Decimals Find each sum or difference. A. 1.8 + 0.2 B. 4 – 0.7 Think: 0.8 + 0.2 = 1. 1.8 + 0.2 = 2 Think: What number added to 0.7 is 1? 4 – 0.7 = 3.3 0.7 + 0.3 = 1 So 1 – 0.7 = 0.3

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Course 1 3-3 Adding and Subtracting Decimals Try This: Example 2 Find each sum or difference. A. 1.6 + 0.4 B. 6 – 0.3 Think: 0.6 + 0.4 = 1. 1.6 + 0.4 = 2.0 Think: What number added to 0.3 is 1? 6 – 0.3 = 5.7 0.3 + 0.7 = 1 So 1 – 0.3 = 0.7

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Course 1 3-3 Adding and Subtracting Decimals Additional Example 3A: Evaluating Decimal Expressions Evaluate 6.73 – x for each value of x. A. x = 3.8 Substitute 3.8 for x. 6.73 – x 6.73 – 3.8 6.73 Align the decimal points. – 3.80 Use a zero as a placeholder. 2.93 Subtract. Place the decimal point.

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Course 1 3-3 Adding and Subtracting Decimals Additional Example 3B: Evaluating Decimal Expressions Evaluate 6.73 – x for each value of x. B. x = 2.9765 Substitute 2.9765 for x. 6.73 – x 6.73 – 2.9765 6.7300 Align the decimal points. –2.9765 Use a zero as a placeholder. 3.7535 Subtract. Place the decimal point.

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Course 1 3-3 Adding and Subtracting Decimals Try This: Example 3A Evaluate 7.58 – x for each value of x. A. x = 3.8 Substitute 3.8 for x. 7.58 – x 7.58 – 3.8 7.58 Align the decimal points. –3.80 Use a zero as a placeholder. 3.78 Subtract. Place the decimal point.

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Course 1 3-3 Adding and Subtracting Decimals Try This: Example 3B Evaluate 8.17 – x for each value of x. B. x = 2.9765 Substitute 2.9765 for x. 8.17 – x 8.17 – 2.9765 8.1700 Align the decimal points. – 2.9765 Use a zero as a placeholder. 5.1935 Subtract. Place the decimal point.

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Lesson Quiz Find each sum or difference. 1. 8.3 + 2.7 2. 9.7 – 4 3. 22.6 + 8.4 4. Evaluate 12.76 – x for x = 8.41. 5. During an ice-skating competition, Dawn received the following scores: 4.8, 5.2, 5.4. What was Dawn’s total score? 5.7 11 Insert Lesson Title Here 31 4.35 Course 1 3-3 Adding and Subtracting Decimals 15.4

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Objective Students will be able to estimate sums and differences (3-5).

Objective Students will be able to estimate sums and differences (3-5).

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