WEBVTT

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珍奈尔正在为公路赛训练

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她的计步器记录了每天她跑的距离

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这是她四天来计步器的读数：

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周六 3.89英里 周日 5.1英里

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周一 10.21英里 周二 3.35英里

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估算四天来她跑的里程数

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然后计算出准确数值

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先来估算一下

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我就把它们都四舍五入取整

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3.89 约等于4英里

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因为十分位上

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是8 大于5

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所以大约就等于4英里

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然后看5.1

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因为1小于5 所以要下舍

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近似为5英里

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10.21 因为2小于5

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要下舍到5英里

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3.35 近似为3英里

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因为3比5小 还是要下舍

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近似成3英里

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如果加起来的话 4+5=9

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9+10=19

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19+3=22

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所以我的估算结果是4天来她跑了22英里

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这是我的估算结果

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下面来计算一下准确数值

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向下拖动点

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3.89+5.1--

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在小数相加的时候一定要注意

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要把小数点对齐

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10.21+3.35

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把这些都加起来

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先看百分位

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第二个数没有百分位 所以9+0+1=10

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10+5=15

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写5 进1

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换个颜色

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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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写5

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进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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写2

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进1

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进位写在上边

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不要误认为是这些加数的一部分

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然后1+1=2

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还要注意

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这里是小数点

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所以她跑过的准确距离是22.55英里

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我们的估算还是比较接近的

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22英里

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跟准确值非常接近

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误差比半英里多一点