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Estimating Sums and Differences with Rounding and Compatible Numbers

Learn how to estimate sums and differences by rounding and using compatible numbers, with examples using whole numbers and decimals.

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Estimating Sums and Differences with Rounding and Compatible Numbers

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  1. Splash Screen

  2. Five-Minute Check (over Lesson 2–1) Main Idea and Vocabulary Example 1: Use Rounding with Whole Numbers Example 2: Use Compatible Numbers Example 3: Use Rounding with Decimals Lesson Menu

  3. I will estimate sums and differences by rounding and using compatible numbers. • estimate • compatible numbers Main Idea/Vocabulary

  4. 923 – 415 Use Rounding with Whole Numbers Estimate 923 – 415 by rounding. Round each number to the nearest hundred. Then subtract. 900 923 is closer to 900 than 1,000. 400 415 is closer to 400 than 500. – 500 Answer:So, 923 – 415 is about 500. Example 1

  5. A B C D Estimate 812 – 376 by rounding. • 400 • 500 • 550 • 600 Example 1

  6. 28.9 – 9.3 Use Compatible Numbers Gareth’s cat weighs 9.3 pounds. Dieter’s dog weighs 28.9 pounds. Use compatible numbers to estimate the difference. Find two numbers that you can easily subtract. 30 28.9 is close to 30. 10 9.3 is close to 10. – 20 Answer:So, the difference is about 20 pounds. Example 2

  7. A B C D Use compatible numbers to estimate the difference 89.3 – 52.2. • 90 • 80 • 50 • 40 Example 2

  8. $ $ $13.95 $13.95 14.00 10.00 + + $ $ 10.00 8.47 8.00 8.47 $ $ Use Rounding with Decimals Karim wants to buy a baseball mitt that costs $13.95 and a baseball that costs $8.47. Estimate the cost of the two items. One Way Another Way Round to the nearest ten. Round to the nearest whole number. + + $20.00 $22.00 Example 3

  9. Use Rounding with Decimals Answer: Depending on how the numbers are rounded, the difference in cost is about $20.00 or $22.00. The actual cost is $22.42. So, rounding to the nearest whole number gave the more accurate estimate. Example 3

  10. A B C D Estimate the difference in the cost of $12.49 and $7.54. • $2.00 • $4.00 • $8.00 • $20.00 Example 3

  11. End of the Lesson End Lesson

  12. Five-Minute Check (over Lesson 2–1) Image Bank Math Tool Chest Add and Subtract Decimals Resources

  13. A B C D (over Lesson 2–1) Round 12,345 to the underlined place. • 12,340 • 12,350 • 12,300 • 12,400 Five Minute Check 1

  14. A B C D (over Lesson 2–1) Round 593.197 to the underlined place. • 593.19 • 593.000 • 593.20 • 593.198 Five Minute Check 2

  15. A B C D (over Lesson 2–1) Round 82.03 to the underlined place. • 82.1 • 83.0 • 82 • 82.04 Five Minute Check 3

  16. A B C D (over Lesson 2–1) Round 9.164 to the underlined place. • 9.2 • 10 • 9.17 • 9 Five Minute Check 4

  17. A B C D (over Lesson 2–1) Round 816.295 to the tenths place. • 816.3 • 816.31 • 816.32 • 816.216 Five Minute Check 5

  18. A B C D (over Lesson 2–1) Round 579.139 to the tens place. • 579.1 • 580 • 580.14 • 580.10 Five Minute Check 6

  19. End of Custom Shows

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