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## 3-3

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**3-3**Adding and Subtracting Decimals Course 1 Warm Up Problem of the Day Lesson Presentation**3-3**Adding and Subtracting Decimals Course 1 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 15**3-3**Adding and Subtracting Decimals Course 1 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.**3-3**Adding and Subtracting Decimals Course 1 Learn to add and subtract decimals.**3-3**Adding and Subtracting Decimals Helpful Hint Estimating before you add or subtract will help you check whether your answer is reasonable. Course 1**3-3**Adding and Subtracting Decimals Course 1 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.**3-3**Adding and Subtracting Decimals Estimate by rounding to the nearest whole number. The total is about 29 points. Course 1 Additional Example 1A: Sports Application A. What was Elise Ray’s total for the events other than the floor exercise? Find the sum of 9.7, 9.425, and 9.85. 9.7 + 9.425 + 9.85 10 + 9 + 10 = 29**3-3**Adding and Subtracting Decimals Align the decimal points. Use zeros as placeholders. Add. Then place the decimal point. Course 1 Additional Example 1A Continued Add. 9.700 9.425 +9.850 28.975 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.**3-3**Adding and Subtracting Decimals Align the decimal points. Use zeros as placeholders. Subtract. Then place the decimal point. Course 1 Additional Example 1B: Sports Application B. How many more points did Elise need on the vault to have a perfect score of 10? Find the difference between 10 and 9.425. 10.000 -9.425 0.575 Elise needed another 0.575 points to have a perfect score.**3-3**Adding and Subtracting Decimals Estimate by rounding to the nearest whole number. The total is about 30 points. Course 1 Try This: Example 1A A. What was Elise Ray’s total for the events other than the vault exercise? Find the sum of 9.8, 9.7, and 9.85. 9.8 + 9.7 + 9.85 10 + 10 + 10 = 30**3-3**Adding and Subtracting Decimals Align the decimal points. Use zeros as placeholders. Add. Then place the decimal point. Course 1 Try This: Example 1A Continued Add 9.800 9.700 +9.850 29.350 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.**3-3**Adding and Subtracting Decimals Align the decimal points. Use zeros as placeholders. Subtract. Then place the decimal point. Course 1 Try This: Example 1B B. How many more points did Elise need on the uneven bars to have a perfect score of 1 Find the difference between 10 and 9.85. 10.00 -9.85 0.15 Elise needed another 0.15 points to have a perfect score.**3-3**Adding and Subtracting Decimals Think: 0.8 + 0.2 = 1. Think: What number added to 0.7 is 1? 0.7 + 0.3 = 1 So 1 – 0.7 = 0.3 Course 1 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 1.8 + 0.2 = 2 4 – 0.7 = 3.3**3-3**Adding and Subtracting Decimals Think: 0.6 + 0.4 = 1. Think: What number added to 0.3 is 1? 0.3 + 0.7 = 1 So 1 – 0.3 = 0.7 Course 1 Try This: Example 2 Find each sum or difference. A. 1.6 + 0.4 B. 6 – 0.3 1.6 + 0.4 = 2.0 6 – 0.3 = 5.7**3-3**Adding and Subtracting Decimals Substitute 3.8 for x. Align the decimal points. Use a zero as a placeholder. Subtract. Place the decimal point. Course 1 Additional Example 3A: Evaluating Decimal Expressions Evaluate 6.73 – x for each value of x. A. x = 3.8 6.73 – x 6.73 –3.8 6.73 – 3.80 2.93**3-3**Adding and Subtracting Decimals Substitute 2.9765 for x. Align the decimal points. Use a zero as a placeholder. Subtract. Place the decimal point. Course 1 Additional Example 3B: Evaluating Decimal Expressions Evaluate 6.73 – x for each value of x. B. x = 2.9765 6.73 – x 6.73 – 2.9765 6.7300 –2.9765 3.7535**3-3**Adding and Subtracting Decimals Substitute 3.8 for x. Align the decimal points. Use a zero as a placeholder. Subtract. Place the decimal point. Course 1 Try This: Example 3A Evaluate 7.58 – x for each value of x. A. x = 3.8 7.58 – x 7.58 – 3.8 7.58 –3.80 3.78**3-3**Adding and Subtracting Decimals Substitute 2.9765 for x. Align the decimal points. Use a zero as a placeholder. Subtract. Place the decimal point. Course 1 Try This: Example 3B Evaluate 8.17 – x for each value of x. B. x = 2.9765 8.17 – x 8.17 – 2.9765 8.1700 – 2.9765 5.1935**3-3**Adding and Subtracting Decimals Course 1 Insert Lesson Title Here 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? 11 5.7 31 4.35 15.4