解题方法
1 . 为了研究网民的上网习惯,某机构随机抽取了年龄在10岁到60岁的网民进行问卷调查,按年龄分为5组,即
,
,
,
,
,并绘制出频率分布直方图,如图所示.若按分层抽样的方法,从上述网民中抽取n人做采访,其中年龄在
中被抽取的人数为7,则![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f3cb8d72bb2e281b943b3b430138ef7.png)
______ .
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4990ce494ad28297532c6e3818f7a4f5.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/8f4b0d8b0cae9a57ba7aa958b2ef572b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/242cfe1efa903a3006579961bea3ddac.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/1720e1256b8eb4fa308d77814edaf197.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/2ab53811235a6aee1c8a7908983b7ce7.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/242cfe1efa903a3006579961bea3ddac.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0f3cb8d72bb2e281b943b3b430138ef7.png)
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