willie815
幼苗
共回答了21个问题采纳率:85.7% 举报
(1)1;(2)
![](https://img.yulucn.com/upload/4/c0/4c08fe75968140fe7ed86e3ce83edcf7_thumb.jpg)
;(3)详见解析.
试题分析:(1)根据平均数计算公式
![](https://img.yulucn.com/upload/a/6c/a6c19eda741addfa53bfe88ba7a614db_thumb.jpg)
,直接由甲、乙两个小组的数学平均成绩相等列式求解
![](https://img.yulucn.com/upload/3/9d/39df13ef2e513fc44bc90710e08c8e74_thumb.jpg)
的值;
(2)分值从
![](https://img.yulucn.com/upload/5/80/5803432934492f31ba5a0242cedc9854_thumb.jpg)
共
![](https://img.yulucn.com/upload/8/43/8430efd8689de63b5c78dda736fc6779_thumb.jpg)
种情况,由(1)中求得的结果可得,当
![](https://img.yulucn.com/upload/d/13/d13caef7a37e981938ef72ba5e0b09da_thumb.jpg)
时,乙组平均成绩超过甲组平均成绩,然后由古典概率模型概率计算公式求概率;
(3)用枚举法列出所有可能的成绩结果,查出两名同学的数学成绩之差的绝对值为
![](https://img.yulucn.com/upload/9/2b/92b807a606d62c64bedf51b2b2914742_thumb.jpg)
的情况数,然后由古典概率模型概率计算公式求概率,然后列分布列,根据公式
![](https://img.yulucn.com/upload/1/e0/1e06db1c68787374af553d9b9e658b58_thumb.jpg)
,此题属于基础题型,关键是读懂题,就能拿满分.
试题解析:(1)依题意,得:
解得
![](https://img.yulucn.com/upload/e/ef/eef04fb9556ece3d7f3d1c7d97335c13_thumb.jpg)
. 3分
(2)设“乙组平均成绩超过甲组平均成绩”为事件
![](https://img.yulucn.com/upload/3/5f/35feaffddeac2a94fbd715f9bf6606ba_thumb.jpg)
,
依题意
![](https://img.yulucn.com/upload/2/1b/21b748d2ea0b8d197a70481e04061ff4_thumb.jpg)
,共有
![](https://img.yulucn.com/upload/8/43/8430efd8689de63b5c78dda736fc6779_thumb.jpg)
种可能.
由(1)可知,当
![](https://img.yulucn.com/upload/e/ef/eef04fb9556ece3d7f3d1c7d97335c13_thumb.jpg)
时甲、乙两个小组的数学平均成绩相同,
所以当
![](https://img.yulucn.com/upload/1/8f/18f997aacbc247894a34db677a236af2_thumb.jpg)
时,乙组平均成绩超过甲组平均成绩,共有
![](https://img.yulucn.com/upload/6/63/663846b7777eea7c988e33b0158cc716_thumb.jpg)
种可能.
因此乙组平均成绩超过甲组平均成绩的概率
![](https://img.yulucn.com/upload/c/1a/c1a4d2907310617ea70c180b52970b18_thumb.jpg)
. 7分
(3)当
![](https://img.yulucn.com/upload/3/27/327b8cdf5bf944261ef1537676646132_thumb.jpg)
时,分别从甲、乙两组同学中各随机选取一名同学,所有可能的成绩结果有
![](https://img.yulucn.com/upload/e/91/e91d051aa97e05c93d3f412370baa98e_thumb.jpg)
种, 它们是:
![](https://img.yulucn.com/upload/7/7e/77e2bfddbdc7f1d5b16797f5d2c905b2_thumb.jpg)
,
![](https://img.yulucn.com/upload/8/d0/8d0c94405efd88b24c150609a96ecf0a_thumb.jpg)
,
![](https://img.yulucn.com/upload/c/04/c04186042eb6a5a5716ef4b2ef9988f0_thumb.jpg)
,
![](https://img.yulucn.com/upload/4/1d/41d68386128136d6caa02089a1f2c6fd_thumb.jpg)
,
![](https://img.yulucn.com/upload/1/53/1534364adbcd5d27671211dc36403e34_thumb.jpg)
,
![](https://img.yulucn.com/upload/4/84/4843a5a594f7b7aeb37454d1e57855d2_thumb.jpg)
,
![](https://img.yulucn.com/upload/4/1d/41d68386128136d6caa02089a1f2c6fd_thumb.jpg)
,
![](https://img.yulucn.com/upload/1/53/1534364adbcd5d27671211dc36403e34_thumb.jpg)
,
则这两名同学成绩之差的绝对值
![](https://img.yulucn.com/upload/9/2b/92b807a606d62c64bedf51b2b2914742_thumb.jpg)
的所有取值为
因此
![](https://img.yulucn.com/upload/f/b7/fb70bd375150d21ff791fd0b7dd463a8_thumb.jpg)
,
![](https://img.yulucn.com/upload/f/a2/fa2e10ce543e9c891be886f41cc5a8c5_thumb.jpg)
,
![](https://img.yulucn.com/upload/b/f3/bf3c9797f69a8d47000148a6f2e31bc7_thumb.jpg)
,
![](https://img.yulucn.com/upload/4/b4/4b41f09627ef2233e5ebef881b5b22ac_thumb.jpg)
,
![](https://img.yulucn.com/upload/f/6c/f6ce906a6743556b7dcfcf8fb43c205a_thumb.jpg)
. 10分
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