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

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

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

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

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

Course Adding and Subtracting Decimals Carly Patterson’s Preliminary Scores EventPoints Floor exercise9.7 Balance beam9.7 Vault9.3 Uneven bars9.45 At the 2004 U.S. Gymnastics Championships, Carly Patterson and Courtney Kupets tied for the All-Around title. To find the total number of points, you add all of the scores.

Course Adding and Subtracting Decimals Additional Example 1A: Sports Application What was Carly Patterson’s total for the events other than the floor exercise? Estimate by rounding to the nearest whole number The total is about 28 points = 28 Find the sum of 9.7, 9.3, and 9.45.

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 28, the answer is reasonable. Carly Patterson’s total for the events other than the floor exercise was

Course Adding and Subtracting Decimals Additional Example 1B: Sports Application How many more points did Carly 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. Carly needed another 0.7 of a point to have a perfect score. Find the difference between 10 and 9.3.

Course Adding and Subtracting Decimals Check It Out: Example 1A What was Carly Patterson’s total for the events other than the vault exercise? Estimate by rounding to the nearest whole number The total is about 29 points = 29 Find the sum of 9.7, 9.7, and 9.45.

Course Adding and Subtracting Decimals Check It Out: 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. Carly Patterson’s total for the events other than the vault exercise was

Course Adding and Subtracting Decimals Check It Out: Example 1B How many more points did Carly need on the uneven bars to have a perfect score of 10? Align the decimal points.Use zeros as placeholders.Subtract. Then place the decimal point. Carly needed another 0.55 of a point to have a perfect score. Find the difference between 10 and 9.45.

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: = = 2.0 Think: What number added to 0.7 is 1? 4 – 0.7 = = 1 So 1 – 0.7 = 0.3

Course Adding and Subtracting Decimals Check It Out: 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

Course Adding and Subtracting Decimals Additional Example 3A: Evaluating Decimal Expressions Evaluate 6.73 – x for each value of x. 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.

Course Adding and Subtracting Decimals You can place any number of zeros at the end of a decimal number without changing its value. Helpful Hint

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

Course Adding and Subtracting Decimals Check It Out: Example 3A Evaluate 7.58 – x for each value of x. 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.

Course Adding and Subtracting Decimals Check It Out: Example 3B Evaluate 8.17 – x for each value of x. x = Substitute for x – x 8.17 – Align the decimal points. – Use zeros as placeholders Subtract. Place the decimal point.

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