解题方法
1 . 某部门为了解青少年视力发展状况,从全市体检数据中,随机抽取了
名男生和
名女生的视力数据.分别计算出男生和女生从小学一年级(
年)到高中三年级(
年)每年的视力平均值,如图所示.
![](https://img.xkw.com/dksih/QBM/editorImg/2022/10/13/a71b06f3-fd47-42da-a035-39d1d8172c4c.png?resizew=497)
(1)从
年到
年中随机选取
年,求该年男生的视力平均值高于上一年男生的视力平均值的概率;
(2)从
年到
年这
年中随机选取
年,设其中恰有
年女生的视力平均值不低于当年男生的视力平均值.求
的分布列和数学期望:
(3)由图判断,这
名学生的视力平均值从哪年开始连续三年的方差最小?(结论不要求证明)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0efba7147f5b9ced8bc4a72f0a9fb8af.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0efba7147f5b9ced8bc4a72f0a9fb8af.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb8b5f0ffe0a3eec01f91f2e9a5db687.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/151e5633a5d0cc30b254167e3dda5803.png)
![](https://img.xkw.com/dksih/QBM/editorImg/2022/10/13/a71b06f3-fd47-42da-a035-39d1d8172c4c.png?resizew=497)
(1)从
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d37eae8a3cf8ef8a44162c82a7229a6a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/151e5633a5d0cc30b254167e3dda5803.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/bdaa19de263700a15fcf213d64a8cd57.png)
(2)从
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cb8b5f0ffe0a3eec01f91f2e9a5db687.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/151e5633a5d0cc30b254167e3dda5803.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8da45c443af7994a26ffa9d8894e7262.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/61128ab996360a038e6e64d82fcba004.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f022950e0faa45b617d497b01b5292b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f022950e0faa45b617d497b01b5292b9.png)
(3)由图判断,这
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/90dd550e1ad9bbf01687ffb4aab788ec.png)
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