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Rounding and Compatible Numbers

Rounding and Compatible Numbers. 5.4 the student is expected to use strategies, including rounding and compatible numbers to estimate solutions to addition, subtraction, multiplication, and division problems. ROUND 7 TO THE NEAREST 10. ROUND 34 TO THE NEAREST 10. 35. 34. 36. 37. 33.

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Rounding and Compatible Numbers

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  1. Rounding and Compatible Numbers 5.4 the student is expected to use strategies, including rounding and compatible numbers to estimate solutions to addition, subtraction, multiplication, and division problems

  2. ROUND 7 TO THE NEAREST 10

  3. ROUND 34 TO THE NEAREST 10 35 34 36 37 33 32 38 31 39 30 40

  4. ROUND 175 TO THE NEAREST 100 150 140 160 130 170 120 180 110 190 100 200

  5. ROUND 123 TO THE NEAREST 100 150 140 160 130 170 120 180 110 190 100 200

  6. Round the number 83 to the nearest 10. First mark the two tens that the number falls between. Then mark the halfway point between the two tens, which we know is 5. Start at 80 and hop to 83, if it is before the halfway point, hop back to 80, if it is after the halfway point, hop forward to 90. 80 81 82 83 84 85 86 87 88 89 90 Round the number 86 to the nearest 10. Start at 80 and hop to 86, if it is before 85 hop back to 80, if it is after 85 hop forward to 90.

  7. A vertical number line also works in the same way and would resemble a thermometer or climbing a ladder. 70 69 Climb the ladder, if you don’t make it to the halfway point you fall back down. If you make it to the halfway point or more you climb on up. 68 Round 64 to the nearest 10 67 66 65 64 63 62 61 60

  8. We like to chant the following poem while rounding: 4 or less, let it rest 5 or more, add one more Zero’s after the line So what we do is underline the place that we are rounding to, that’s the line, draw an arrow to the number to the right of the line, he’s the boss and tells the underlined number what to do. For example:

  9. I want to round the number 53 to the nearest 10. Underline the 5 and draw an arrow to the 3. 5 3 The 3 tells the 5 what to do. Say the chant: 4 or less, let it rest (it is the underlined number) 5 or more, add one more Zero’s after the line. Since 3 is 4 or less, we would let it rest, which means the 5 remains the same. Zeroes after the line, 1 place after the line, 1 zero +0 5 3 5 0

  10. I want to round the number 58 to the nearest 10. Underline the 5 and draw an arrow to the 8. 5 8 The 8 tells the 5 what to do. Say the chant: 4 or less, let it rest (it is the underlined number) 5 or more, add one more Zero’s after the line. Since 8 is 5 or more, we would add one more and the 5 becomes a 6. Zeroes after the line, 1 place after the line, 1 zero +1 5 8 6 0

  11. 5.4 the student is expected to use strategies, including rounding and compatible numbers to estimate solutions to addition, subtraction, multiplication, and division problems

  12. Mathematicians sometimes estimate answers to multiplication and division prob­lems by using compatible numbers. Compatible numbers are numbers that work well together. Mathematicians sometimes estimate using compatible numbers. Compatible numbers work well together or are easy to manipulate in your head. The most common examples are to make 10’s or 100’s. They give you a rough estimate of where your answer should be. It is not rounding, it is simply grouping numbers together that work nicely together to make the problem easier.

  13. A compatible number is a number that is easy to use when answering an arithmetic question. Example 53+67 The compatible number for 53 would be 50 and the compatible number for 67would be 70. 50 and 70 are easier to add than 53 and 67. Example38 - 23A compatible number for 38 is 40A compatible number for 23 is 20 (or 25)The difference of the compatible numbers would be 20 (or 15). So you know the answer will be near there.

  14. Compatible numbers are also numbers that are easy to put together, say to make a 10, to make addition or subtraction easier. Say you are adding 3 + 5 + 6 + 7 + 4If you combine 3 + 7 = 10  &  6 + 4 = 10, you then have 10 + 10 + 5 = 25

  15. Multiplication example A page in my chapter book has 12 words in each line and 32 lines on the page. About how many words are on the whole page? Change 12 and 32 to nearby numbers that are easier to multiply in your head. 12 is close to 10. 32 is close to 30. 10 x 30 = 300, so the book has about 300 words.

  16. Multiplication example A delivery truck is carrying 80 televisions in individual boxes. Each box weighs between 26 and 37 pounds. Which of the following is a reasonable estimate of the total weight of the boxes? Change 26 and 37 to nearby numbers that are easier to multiply in your head. 26 is close to 30. 37 is close to 40. 80 is already a friendly number so we don’t have to change it. 30 x 80 = 2,400, and 40 x 80 = 3,200, so the a reasonable estimate of the total weight is between 2,400 and 3,200.

  17. Division example Mr. Gomez had 396 crayons left over at the end of the year. He’s putting them in bags to send home with the kids. He has 20 students in his class. About how many crayons will each student get? Change 396 to a nearby number that is easier to divide by 20. 396 is close to 400. 20 is already a friendly number. You don’t always have to change both numbers. 400 ÷ 20 = 20, so each student will get about 20 crayons.

  18. multiplication example 21 × 19 21 is close to _______. 19 is close to _______. _______ × _______ = _______, so the answer is about _______.

  19. division example 249 ÷ 24 249 is close to _______. 24 is close to _______. _______ ÷ _______ = _______, so the answer is about _______.

  20. Presented by: Lorrie Ballinger--Lundy Charlotte Finley--Green/Western Hills Mary Henderson--Polk

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