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Warm Up

Preview. Warm Up. California Standards. Lesson Presentation. Warm Up Estimate by rounding to the nearest integer. 1. 3.62 + 4.1 2. 8.23 – 7.47 3. 8.52 – 3.16 4. 5.826 + 11.729 Multiply. 8. 1. 6. 18. 5. 842  76. 63,992. 6. 1,240  83. 102,920. 7. 821  712. 584,552.

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Warm Up

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  1. Preview Warm Up California Standards Lesson Presentation

  2. Warm Up Estimate by rounding to the nearest integer. 1.3.62 + 4.1 2. 8.23 – 7.47 3. 8.52 – 3.16 4. 5.826 + 11.729 Multiply. 8 1 6 18 5. 842  76 63,992 6.1,240  83 102,920 7. 821  712 584,552 8. 302  15 4,530

  3. California Standards Extension of NS2.3 Solve addition, subtraction, multiplication, and divisionproblems, including those arising in concrete situations, that use positive and negative integers and combinations of these operations.

  4. Objective: You will learn how to add, subtract, and multiply decimals.

  5. One of the coolest summers on record in the Midwest was in 1992. The average summertime temperature that year was 66.8°F. Normally, the average temperature is 4°F higher than it was in 1992. To find the normal average summertime temperature in the Midwest, you can add 66.8°F and 4°F.

  6. 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. The normal average summertime temperature in the Midwest is 70.8°F.

  7. Example 1: Adding and Subtracting Decimals Add. Estimate to check whether the answer is reasonable. Estimate 4.55 + 11.3

  8. Example 2: Adding and Subtracting Decimals Subtract. Estimate to check whether the answer is reasonable. Estimate 28 – 15.911

  9. Check It Out! Example 3 Add. Estimate to check whether the answer is is reasonable. Estimate 6.78 + 13.2

  10. Check It Out! Example 4 Subtract. Estimate to check whether the answer is reasonable. Estimate 34 – 12.462

  11. 7  8 56 0.7  0.8 + Same digits To multiply decimals, multiply as you would with integers, and then place the decimal point. The product should have the same number of decimal places as the sum of the decimal places in the factors. 1 decimal place 1 decimal place 0. 56 2 decimal places

  12. Example 5: Multiplying Decimals Multiply. Estimate to check whether the answer is reasonable. Estimate 2.4  2

  13. Check It Out! Example 6 Multiply. Estimate to check whether the answer is reasonable. Estimate 3.2  1.6

  14. Example 7: Application To find your weight on another planet, multiply the relative gravitational pull of the planet and your weight. The relative gravitational pull on Mars is 0.38. What would a person who weighs 85 pounds on Earth weigh on Mars? The person would weigh 32.3 pounds on Mars.

  15. Check It Out! Example 8 Jet fuel weighs approximately 6.2 pounds per gallon. If a plane was serviced with 1,012 gallons of fuel, how many pounds of fuel were used? A plane would use 6,274.4 pounds of fuel.

  16. –3.84  0.9 Example 7: Multiplying Decimals Multiply. Estimate to check whether the answer is reasonable. –3.84  0.9 2 decimal places 1 decimal place –3.456 2 + 1 = 3 decimal places Estimate –3.456 is a reasonable answer. –4  1 = –4

  17. –2.96  0.7 Check It Out! Example 2B Multiply. Estimate to check whether the answer is reasonable. –2.96  0.7 2 decimal places 1 decimal place –2.072 2 + 1 = 3 decimal places Estimate –2.072 is a reasonable answer. –3  1 = –3

  18. Lesson Quiz Add, subtract, or multiply.Estimate to check whether your answer is reasonable. 21.25; Estimate: 7 + 14 = 21 1. 6.98 + 14.27 6.72 – 4.16 2.56; Estimate: 7 – 4 = 3 2. 3. 3.4  4.1 4. 7.62  (–5.4) 5. Dennis runs 7.2 miles per day. How far does he run in 5 days? 13.94; Estimate: 3 • 4 = 12 –41.148; Estimate: 8 • (–5) = –40 36 miles

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