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Lesson Objective: To be able to round numbers
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What is rounding? Sometimes we want to add numbers in our head but the numbers are a bit tricky. We can estimate (take a good guess) the answer It is easier if we use numbers that are in more usable forms. Rounding means we ignore some of the less significant digits.
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Up or Down Does the number end in… Round down 1, 2, 3, 4
5, 6, 7, 8, 9 Round up
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Lets look at a number line…
Where do these numbers go? 64 21 39 83
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Let’s take a closer look…
21 Is 21 closer to 20 or 30? Does it end in 1, 2, 3 or 4?
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Round down!
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Another close look… Is 39 closer to 30 or 40?
Does it end in 5, 6, 7, 8 or 9?
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Round up!
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Another close look… Is 64 closer to 60 or 70?
Does it end in 1, 2, 3 or 4?
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Round down!
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Another close look… Is 83 closer to 80 or 90?
Does it end in 1, 2, 3 or 4?
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Round down!
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32
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Round down! 30
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97
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Round up! 100
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5
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Round up! 10
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71
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Round down! 70
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Round to the nearest thousand
512827
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Round Up 513000
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