 ## Presentation on theme: "Adding and Subtracting Decimals"— Presentation transcript:

Course 2 3-2 Adding and Subtracting Decimals Do Now Estimate by rounding to the nearest integer. (–8.23) – 3.16 8 –1 6 18 Hwk: p 25, 26

Course 2 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. 0.5 7 4.625 8.75 6.375 5.25 4 2.25 2.875

Course 2 3-2 Adding and Subtracting Decimals EQ: How do I add/subtract/multiply/divide decimals? M7N1.c Add, subtract, multiply, and divide positive and negative rational numbers

Course 2 3-2 Adding and Subtracting Decimals Add 66.8 and 4 66.8 + 4.0 Use zero as a placeholder so that both numbers have the same number of digits after their decimal points. 70.8 Add each column just as you would add integers. Line up the decimal points.

Course 2 3-2 Adding and Subtracting Decimals 4.55 15.85 Estimate = 16

Course 2 3-2 Adding and Subtracting Decimals 6.44 22.44 Estimate = 22

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

Course 2 3-2 Adding and Subtracting Decimals – (–10.972) Estimate –8 + (–11) = –19

Course 2 3-2 Adding and Subtracting Decimals 19.98 Estimate = 20

Course 2 3-2 Adding and Subtracting Decimals 38.21 Estimate = 38

Course 2 3-2 Adding and Subtracting Decimals – (–13.852) = –21.742 Estimate –8 + (–14) = –22

Course 2 3-2 Adding and Subtracting Decimals A – 2.08 3.26 B. 28 – 28.000 –15.911 12.089

Course 2 3-2 Adding and Subtracting Decimals A – 1.46 2.11 B. 34 – 34.000 –12.462 21.538

Course 2 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? The total number of trips was million.

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Course 2 3-2 Adding and Subtracting Decimals Insert Lesson Title Here 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? The total number of bushels was million.

7  8 56 0.7  0.8 0. 56 3-3 Multiplying Decimals 1 decimal place
Course 2 3-3 Multiplying Decimals To multiply decimals, multiply as you would with integers. To place the decimal point in the product, count the number of decimal places in each factor. The product should have the same number of decimal places in the factors. 7  8 56 0.7  0.8 1 decimal place 1 decimal place + 0. 56 2 decimal places Same digits

Additional Example 1: Multiplying Integers by Decimals
Course 2 3-3 Multiplying Decimals Additional Example 1: Multiplying Integers by Decimals Multiply. A. 7 · 0.1 7  0.1 0.7 B. –3 · 0.03 –3  0.03 – 0.09

Additional Example 1: Multiplying Integers by Decimals
Course 2 3-3 Multiplying Decimals Additional Example 1: Multiplying Integers by Decimals Multiply. C · 35 2.45  35 12 25 85.75

3-3 Multiplying Decimals Check It Out: Example 1 Multiply. A. 8 · 0.3
Course 2 3-3 Multiplying Decimals Check It Out: Example 1 Multiply. A. 8 · 0.3 8  0.3 2.4 B. –2 · 0.04 –2  0.04 –0.08

3-3 Multiplying Decimals Check It Out: Example 1 Multiply.
Course 2 3-3 Multiplying Decimals Check It Out: Example 1 Multiply. C · 15 3.65  15 18 25 54.75

Additional Example 2A: Multiplying Decimals by Decimals
Course 2 3-3 Multiplying Decimals Additional Example 2A: Multiplying Decimals by Decimals Multiply. 2.4 · 1.8 2.4  1.8 1 92 + 2 40 4.32 Estimate 2 · 2 = 4

Additional Example 2B: Multiplying Decimals by Decimals
Course 2 3-3 Multiplying Decimals Additional Example 2B: Multiplying Decimals by Decimals Multiply. –3.84 · 0.9 –3.84  0.9 –3.456 Estimate –4 · 1 = –4

3-3 Multiplying Decimals Check It Out: Example 2A Multiply. 3.2 · 1.6
Course 2 3-3 Multiplying Decimals Check It Out: Example 2A Multiply. 3.2 · 1.6 3.2  1.6 1 92 + 3 20 5.12 Estimate 3 · 2 = 6

3-3 Multiplying Decimals Check It Out: Example 2B Multiply.
Course 2 3-3 Multiplying Decimals Check It Out: Example 2B Multiply. –2.96 · 0.7 –2.96  0.7 –2.072 Estimate –3 · 1 = –3

Adding and Subtracting Decimals Insert Lesson Title Here
Course 2 3-2 Adding and Subtracting Decimals Insert Lesson Title Here Quiz 1. 2. – (–19.2) 21.25; –27.66; Subtract. 3. 6.72 – 4.16 4. 24 – 3.8 2.56; 20.2;

Adding and Subtracting Decimals Insert Lesson Title Here
Course 2 3-2 Adding and Subtracting Decimals Insert Lesson Title Here Quiz Subtract. 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. 1.41 seconds;

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Course 2 3-3 Multiplying Decimals Insert Lesson Title Here Lesson Quiz Multiply. 6. 9 · 0.7 · 1.5 · 4.1 · (–5.4) 10. Dennis runs 7.2 miles per day. How far does he run in 5 days? 6.3 2.4 13.94; –41.148; 36 miles