3-2 Adding and Subtracting Decimals Warm Up Warm Up Lesson Presentation Lesson Presentation Problem of the Day Problem of the Day Lesson Quizzes Lesson Quizzes

3-2 Adding and Subtracting Decimals Warm Up Estimate by rounding to the nearest integer (–8.23) – –1 6 18

3-2 Adding and Subtracting Decimals Problem of the Day Complete the magic square. The sum of each row, column, and diagonal must be the same number

3-2 Adding and Subtracting Decimals Learn to add and subtract decimals.

3-2 Adding and Subtracting Decimals One of the coolest summers on record in the Midwest was in The average summertime temperature that year was 66.8°F. Normally, the average temperature is 4°F higher than it was in To find the normal average summertime temperature in the Midwest, you can add 66.8°F and 4°F.

3-2 Adding and Subtracting Decimals Use zero as a placeholder so that both numbers have the same number of digits after their decimal points. Add each column just as you would add integers. Line up the decimal points The normal average summertime temperature in the Midwest is 70.8°F.

3-2 Adding and Subtracting Decimals Add. Estimate to check whether each answer is is reasonable Line up the decimal points. Use zero as a placeholder Add. Estimate = is a reasonable answer. Additional Example 1A: Adding Decimals

3-2 Adding and Subtracting Decimals Add. Estimate to check whether each answer is is reasonable Line up the decimal points. Use zeros as placeholders Add. Estimate = is a reasonable answer. Additional Example 1B: Adding Decimals

3-2 Adding and Subtracting Decimals When adding numbers with the same sign, find the sum of their absolute values. Then use the sign of the numbers. Remember!

3-2 Adding and Subtracting Decimals Add. Estimate to check whether each answer is reasonable. – ( – ) Think: Line up the decimal points. Add. – ( – ) = – Use the sign of the two numbers. Additional Example 1C: Adding Decimals Use zero as a placeholder Estimate – 8 + ( – 11) = – 19 – is a reasonable answer.

3-2 Adding and Subtracting Decimals Add. Estimate to check whether each answer is is reasonable Line up the decimal points. Use zero as a placeholder Add. Estimate = is a reasonable answer. Check It Out: Example 1A

3-2 Adding and Subtracting Decimals Add. Estimate to check whether each answer is is reasonable Line up the decimal points. Use zeros as placeholders Add. Estimate = is a reasonable answer. Check It Out: Example 1B

3-2 Adding and Subtracting Decimals Add. Estimate to check whether each answer is reasonable. – ( – ) Think: Line up the decimal points. Add. – ( – ) = – Use the sign of the two numbers. Check It Out: Example 1C Use zero as a placeholder Estimate – 8 + ( – 14) = – 22 – is a reasonable answer.

3-2 Adding and Subtracting Decimals Subtract. A – Line up the decimal points. – Subtract. Additional Example 2: Subtracting Decimals B. 28 – Use zeros as placeholders. – Subtract Line up the decimal points.

3-2 Adding and Subtracting Decimals Subtract. A – Line up the decimal points. – Subtract. Check It Out: Example 2 B. 34 – Use zeros as placeholders. – Subtract Line up the decimal points.

3-2 Adding and Subtracting Decimals During one month in the United States, million commuter trips were taken on buses, and million commuter trips were taken on light rail. What was the total number of trips taken on buses and light rail? Estimate to check whether your answer is reasonable. Line up the decimal points. Use zero as a place holder Add = is a reasonable answer. Estimate The total number of trips was million. Additional Example 3: Application

3-2 Adding and Subtracting Decimals Check It Out: Example 3 Line up the decimal points. Use zero as a place holder Add = 314 Estimate The total number of bushels was million. In 1999, million bushels of corn were grown in the United States. In 2000, the harvest yielded million bushels. What was the total production for those two years? Estimate to check whether your answer is reasonable.

3-2 Adding and Subtracting Decimals Standard Lesson Quiz Lesson Quizzes Lesson Quiz for Student Response Systems

3-2 Adding and Subtracting Decimals Lesson Quiz: Part I 2.56; Estimate: 7 – 4 = ; Estimate: = 21 –27.66; Estimate: -8 + (-19) = – ; Estimate: = 20 Add. Estimate to check whether your answer is reasonable – ( – 19.2) – 4.16 Subtract. Estimate to check whether your answer is reasonable.

3-2 Adding and Subtracting Decimals Lesson Quiz: Part II Subtract. Estimate to check whether your answer is reasonable. 5. Renee finished her first lap in the 200 m freestyle event in seconds. She completed the second lap in seconds. By how much did her time increase in the second lap? Estimate to check whether your answer is reasonable seconds; Estimate: 30 – 29 = 1

3-2 Adding and Subtracting Decimals 1. Identify the sum and then estimate to check whether the answer is reasonable A ; estimate: = 20 B ; estimate: = 20 C ; estimate: = 19 D ; estimate: = 19 Lesson Quiz for Student Response Systems

3-2 Adding and Subtracting Decimals 2. Identify the sum and then estimate to check whether the answer is reasonable. – (–18.1) A. –8.78; estimate: –9 + (–18) = –9 B. –27.42; estimate: –9 + (–18) = –9 C. –27.42; estimate: –9 + (–18) = –27 D. –8.78; estimate: –9 + (–18) = –27 Lesson Quiz for Student Response Systems

3-2 Adding and Subtracting Decimals 3. Identify the difference and then estimate to check whether the answer is reasonable – 3.25 A. 4; estimate: 7 – 3 = 4 B. 4.22; estimate: 7 – 3 = 4 C. 4.32; estimate: 8 – 3 = 5 D. 4.38; estimate: 8 – 3 = 5 Lesson Quiz for Student Response Systems

3-2 Adding and Subtracting Decimals 4. Identify the difference and then estimate to check whether the answer is reasonable. 35 – 2.7 A. 32; estimate: 35 – 3 = 32 B. 32.3; estimate: 35 – 3 = 32 C. 33; estimate: 35 – 2 = 33 D. 33.3; estimate: 35 – 2 = 33 Lesson Quiz for Student Response Systems

3-2 Adding and Subtracting Decimals 5. Margaret took an exam that has two parts. She completed the first part in minutes and the second part in minutes. By how much did her time increase in the second part? Estimate to check whether the answer is reasonable. A. 16 min; estimate: 33 – 17 = 16 B min; estimate: 32 – 17 = 15 C min; estimate: 32 – 18 = 14 D. 10 min; estimate: 30 – 20 = 10 Lesson Quiz for Student Response Systems