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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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Presentation on theme: "3-3 Adding and Subtracting Decimals Course 1 Warm Up Warm Up Lesson Presentation Lesson Presentation Problem of the Day Problem of the Day."— Presentation transcript:

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

2 Warm Up Estimate by rounding to the indicated place value ; ones – 21.82; tenths Estimate each product or quotient  ÷ Course Adding and Subtracting Decimals 15

3 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 , 24 divided by 3 is 8, and 438 is the only number with 8 as a digit. Course Adding and Subtracting Decimals

4 Learn to add and subtract decimals. Course Adding and Subtracting Decimals

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

6 Course 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.

7 Course 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 The total is about 29 points = 29 Find the sum of 9.7, 9.425, and 9.85.

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

9 Course 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? Align the decimal points.Use zeros as placeholders.Subtract. Then place the decimal point. Elise needed another points to have a perfect score. Find the difference between 10 and

10 Course 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 The total is about 30 points = 30 Find the sum of 9.8, 9.7, and 9.85.

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

12 Course 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 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.

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

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

15 Course 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 – x 6.73 – Align the decimal points. – 3.80 Use a zero as a placeholder Subtract. Place the decimal point.

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

17 Course 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 – x 7.58 – Align the decimal points. –3.80 Use a zero as a placeholder Subtract. Place the decimal point.

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

19 Lesson Quiz Find each sum or difference – Evaluate – x for x = During an ice-skating competition, Dawn received the following scores: 4.8, 5.2, 5.4. What was Dawn’s total score? Insert Lesson Title Here Course Adding and Subtracting Decimals 15.4


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