解题方法
1 . 某市对新形势下的中考改革工作进行了全面的部署安排. 中考录取科目设置分为固定赋分科目和非固定赋分科目,固定赋分科目(语文、数学、英语、物理、体育与健康)按卷面分计算;非固定赋分科目(化学、生物、道德与法治、历史、地理)按学生在该学科中的排名进行等级赋分,即根据改革方案,将每门等级考试科目中考生的原始成绩从高到低分为A,
,
,
,
,
,
,
共
个等级. 参照正态分布原则,确定各等级人数所占比例分别为
,
,
,
,
,
,
,
. 等级考试科目成绩计入考生总成绩时,将A至
等级内的考生原始成绩,依照等比例转换法则,分别转换到
,
,
,
,
,
,
,
八个分数区间,得到考生的等级成绩. 该市学生的中考化学原始成绩制成频率分布直方图如图所示:
![](https://img.xkw.com/dksih/QBM/2022/4/13/2957147482324992/2957395828621312/STEM/7f8d5784-de28-40a4-a8c2-2103bfaf23cf.png?resizew=265)
(1)求图中
的值;
(2)估计该市学生中考化学原始成绩不少于多少分才能达到
等级及以上(含
等级)?
(3)由于中考改革后学生各科原始成绩不再返回学校,只告知各校参考学生的各科平均成绩
及方差
. 已知某校初三共有
名学生参加中考,为了估计该校学生的化学原始成绩达到
等级及以上(含
等级)的人数
,将该校学生的化学原始成绩
看作服从正态分布
,并用这
名学生的化学平均成绩
作为
的估计值,用这
名学生化学成绩的方差
作为
的估计值,计算人数
(结果保留整数).
附:
,
,
.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5a8a5d766aad11b1c32dabf6e3eada26.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/7f9e8449aad35c5d840a3395ea86df6d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2882b9baf240d68e92d67dabb12cd332.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c5db41a1f31d6baee7c69990811edb9f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8e194680eeb097a6b5f3b834d3b97688.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8455657dde27aabe6adb7b188e031c11.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/cd3304e23f3b0f9569c4140ca89b6498.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/63b971b2c43a814d35dfe0c1be4c45d9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d9b174b3d5b2b0334586fda178eb78c3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/373c1c49ac5418e539146545c01c7188.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/17058aeec59cbfa95f9bef08240f4344.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/17058aeec59cbfa95f9bef08240f4344.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/373c1c49ac5418e539146545c01c7188.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d9b174b3d5b2b0334586fda178eb78c3.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/63b971b2c43a814d35dfe0c1be4c45d9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2a30f3a8b673cc28bd90c50cf1a35281.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/13a0dc3b0349c53d7bf36dfe97958cea.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a40cf767fd2a684f2f1ed9216836792.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f58d9a123e465dace224231f54ee94e8.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8826cd3a88388c3896b1e429fabd437f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/627a86a6ccc6968f95c9e26db5c4b80d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1720e1256b8eb4fa308d77814edaf197.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/242cfe1efa903a3006579961bea3ddac.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8f4b0d8b0cae9a57ba7aa958b2ef572b.png)
![](https://img.xkw.com/dksih/QBM/2022/4/13/2957147482324992/2957395828621312/STEM/7f8d5784-de28-40a4-a8c2-2103bfaf23cf.png?resizew=265)
(1)求图中
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0a6936d370d6a238a608ca56f87198de.png)
(2)估计该市学生中考化学原始成绩不少于多少分才能达到
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5a8a5d766aad11b1c32dabf6e3eada26.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5a8a5d766aad11b1c32dabf6e3eada26.png)
(3)由于中考改革后学生各科原始成绩不再返回学校,只告知各校参考学生的各科平均成绩
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/c85481cd7e94130ef3aa05b4a39e79cd.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/671f43c79d612c93a6d160335e86e177.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dadc63e6e33743ce590ed968948a5a58.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5a8a5d766aad11b1c32dabf6e3eada26.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/5a8a5d766aad11b1c32dabf6e3eada26.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0d8b9ad2fcfff3dd546c5fdbedfe6238.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f022950e0faa45b617d497b01b5292b9.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/a437a6c5efe0d5cbc9b0ed2a3a861c22.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dadc63e6e33743ce590ed968948a5a58.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ecf07ca7caa6e0d7dfa54a3bf6af4529.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1100379a4385b9ce064847bc21760adc.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/dadc63e6e33743ce590ed968948a5a58.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/ea96894fba348abdc757bf22dcd26f52.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/742d3e642d52e01899f66df411100838.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0d8b9ad2fcfff3dd546c5fdbedfe6238.png)
附:
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e97705bedd45b860523d4fac71b64100.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/491c4b275f466e0ef3d15d61e471e34d.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/3280373a54d4b00138c803698ec60b74.png)
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