Module 1 Lesson 8 Place Value, Rounding, and Algorithms for Addition and Subtraction

# Module 1 Lesson 8 Place Value, Rounding, and Algorithms for Addition and Subtraction

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## Module 1 Lesson 8 Place Value, Rounding, and Algorithms for Addition and Subtraction

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1. Module 1 Lesson 8Place Value, Rounding, and Algorithms for Addition and Subtraction Topic c: rounding multi-digit whole numbers This PowerPoint was developed by Beth Wagenaar and Katie E. Perkins. The material on which it is based is the intellectual property of Engage NY.

2. Lesson 8 Topic: Rounding Multi-Digit Whole Numbers • Objective: Round multi-digit numbers to any place using the vertical number line V E R T I C A L Horizontal

3. Fluency Practice – Sprint A Lesson 8 Get set! Take your mark! Think!

4. Fluency Practice – Sprint B Lesson 8 Get set! Take your mark! Think!

5. Lesson 8 Rename the Units 3 Minutes for 2 slides 357,468 • Say the number. • How many thousands are in 357,468? • On your whiteboards, fill in the following sentence: • 357,468 = ________ thousands 468 ones 357

6. Lesson 8 Rename the Units 3 Minutes for 2 slides 234,673 • Say the number. • How many ten thousands are in 234,673? • On your whiteboards, fill in the following sentence: • 234,673 = ________ ten thousands 4,673 ones 23

7. Lesson 8 Rename the Units 3 Minutes for 2 slides 357,468 35 357,468 = ________ ten thousands 7,468 ones 3,574 357,468 = ________ hundreds 6 tens 8 ones 35,746 357,468 = ________ tens 8 ones

8. Lesson 8 Application Problem 6 Minutes Jose’s parents bought a used car, a new motorcycle, and a used snowmobile. The car cost \$8,999. The motorcycle cost \$9,690. The snowmobile cost \$4,419. About how much money did they spend on the three items?

9. Lesson 8 Application Problem 6 Minutes

10. Lesson 8 Concept Development 32 Minutes Materials: Personal white boards

11. Lesson 8 Problem 1 Use a vertical line to round a five and six-digit number to the nearest ten thousand 8 ten thousands 80,000 How many ten thousands are in 72,744? And 1 more ten thousand would be? What’s halfway between 7 ten thousands and 8 ten thousands? 7 ten thousands 5 thousands (75,000) Where should I label 72,744? Is 72,744 nearer to 70,000 or 80,000? Therefore we say 72,744 rounded to the nearest ten thousand is 70,000. 72,744 7 ten thousands (70,000)

12. Lesson 8 More of Problem 1 Use a vertical line to round a five and six-digit number to the nearest ten thousand 34 ten thousands 340,000 How many ten thousands are in 337,601? And 1 more ten thousand would be? 337,601 What’s halfway between 33 ten thousands and 34 ten thousands? 33 ten thousands 5 thousands (335,000) Where should I label 337,601? Is 337,601 nearer to 330,000 or 340,000? Therefore we say 337,601 rounded to the nearest ten thousand is 340,000. 33 ten thousands (330,000)

13. Lesson 8 Problem 2 Use a vertical line to round a six-digit number to the nearest hundred thousand How many hundred thousands are in 749,085? 8 hundred thousands 800,000 And 1 more hundred thousand would be? What’s halfway between 7 hundred thousands and 8 hundred thousands? 7 hundred thousands 5 ten thousands (750,000) Where should I label 749,085? Is 749,085 nearer to 700,000 or 800,000? Therefore we say 749,085 rounded to the nearest hundred thousand is 700,000. 749,085 7 hundred thousands (700,000)

14. Lesson 8 More of Problem 2 Use a vertical line to round a six-digit number to the nearest hundred thousand How many hundred thousands are in 908,899? 10 hundred thousands 1,000,000 And 1 more hundred thousand would be? What’s halfway between 9 hundred thousands and 10 hundred thousands? 9 hundred thousands 5 ten thousands (950,000) Where should I label 908,899? Is 908,899 nearer to 900,000 or 1,000,000? Therefore we say 908,899 rounded to the nearest hundred thousand is 900,000. 908,899 9 hundred thousands (900,000)

15. Lesson 8 Problem 3 Estimating with addition and subtraction 505,341 + 193,841 • Without finding the actual answer, I can estimate the answer by rounding each addend to the nearest hundred thousand and then add the rounded numbers.

16. Problem 3 Estimating with addition and subtraction Lesson 8 505,341 + 193,841 500,000 6 hundred thousands 600,000 • Use a number line to round both numbers to the nearest hundred thousand. 5 hundred thousands 5 ten thousands (550,000) 505,341 5 hundred thousands (500,000)

17. Problem 3 Estimating with addition and subtraction Lesson 8 505,341 + 193,841 + 200,000 500,000 2 hundred thousands 200,000 • Use a number line to round both numbers to the nearest hundred thousand. 193,841 1 hundred thousands 5 ten thousands (150,000) 1 hundred thousands (100,000)

18. Problem 3 Estimating with addition and subtraction Lesson 8 505,341 + 193,841 + 200,000 500,000 700,000 • Now add 500,000 + 200,000. • So, what’s a good estimate of the sum of 505,341 and 193,841?

19. Lesson 8 More of Problem 3 35,555 – 26,555 • How can we use rounding to estimate the answer? • Let’s round each number before we subtract. • Discuss with your partner how you will round to estimate the difference.

20. Lesson 8 More of Problem 3 35,555 – 26,555 I can round each number to the nearest ten thousand. That way I’ll have mostly zeros in my numbers. 40,000 minus 30,000 is 10,000.

21. Lesson 8 More of Problem 3 35,555 – 26,555 I chose a different way. I said 35,555 minus 26,555 is like 35 minus 26 which is 9. 35,000 minus 26,000 is 9,000. It’s more accurate to round up. 36,000 minus 27,000 is 9,000.

22. Lesson 8 More of Problem 3 35,555 – 26,555 Hey, it’s the same answer!

23. Lesson 8 More of Problem 3 35,555 – 26,555 Did you discover that it’s easier to find an estimate rounded to the largest unit? Some of us might have rounded up, others down. We got two different estimates!

24. Lesson 8 More of Problem 3 35,555 – 26,555 • Which estimate do you suppose is closer to the actual difference? • How might we find an estimate even closer to the actual difference?

25. Problem Set (10 Minutes)

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35. Student Debrief Lesson 8 • Compare Problems 1(b) and 1(c). How did you determine your endpoints for each number line? • Retell to your partner your steps for rounding a number. Which step is most difficult for you? Why? • How did Problem 1(c) help you to find the missing number possibilities in Problem 4? • Look at Problem 5. How did your estimates compare? What did you notice as you solved? • What are the benefits and drawbacks of rounding the same number to different units (as you did in Problem 5)? • In what real life situation might you make an estimate like Problem 5? • Write and complete one of the following statements in your math journal: • The purpose of rounding addends is _____. • Rounding to the nearest _____ is best when _____. 7 minutes

36. Lesson 1 Math Journal Write and complete the following statements In your math journal: The purpose for rounding addends is _____. Rounding to the nearest _____ is best when _____.

37. Exit Ticket Lesson 8

38. Homework!!

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