WEBVTT

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珍奈爾正在爲公路賽訓練

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她的計步器記錄了每天她跑的距離

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這是她四天來計步器的讀數：

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周六 3.89英裏 周日 5.1英裏

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周一 10.21英裏 周二 3.35英裏

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估算四天來她跑的裏程數

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然後計算出準確數值

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先來估算一下

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我就把它們都四捨五入取整

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3.89 約等於4英裏

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因爲十分位上

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是8 大於5

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所以大約就等於4英裏

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然後看5.1

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因爲1少於5 所以要下舍

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近似爲5英裏

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10.21 因爲2少於5

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要下舍到5英裏

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3.35 近似爲3英裏

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因爲3比5小 還是要下舍

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近似成3英裏

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如果加起來的話 4+5=9

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9+10=19

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19+3=22

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所以我的估算結果是4天來她跑了22英裏

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這是我的估算結果

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下面來計算一下準確數值

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向下拖動點

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3.89+5.1--

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在小數相加的時候一定要注意

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要把小數點對齊

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10.21+3.35

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把這些都加起來

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先看百分位

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第二個數沒有百分位 所以9+0+1=10

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10+5=15

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寫5 進1

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換個顏色

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1+8=9

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9+1=10

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10+2=12

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12+3=15

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寫5

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進1

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1+3=4

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4+5=9

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9+0=9

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9+3=12

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寫2

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進1

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進位寫在上邊

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不要誤認爲是這些加數的一部分

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然後1+1=2

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還要注意

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這裡是小數點

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所以她跑過的準確距離是22.55英裏

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我們的估算還是比較接近的

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22英裏

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跟準確值非常接近

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誤差比半英裏多一點