名校
1 . 将连续正整数1,2,3,
,
从小到大排列构成一个
,
为这个数的位数.例如:当
时,此时为123456789101112,共有15个数字,则
.现从这个数中随机取一个数字,
为恰好取到0的概率.
(1)求
;
(2)当
时,求
得表达式;
(3)令
为这个数中数字0的个数,
为这个数中数字9的个数,
,
,求当
时,
的最大值.
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/daa5e9bd516f6282483b92cfe6074623.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/4673710cd589e1b6cd3d2906e36791df.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/df313df25c54af0180e52424f480260b.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/081fad2749f3f201cf2c324c3d0dd190.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/aadc4f26938f7a9d55006ab4d3c1e102.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/d6df056ae0ceeac78f539e23aadd6fcd.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e6291d7b91f71daa0b3c4fa02dc7a5ea.png)
(1)求
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/0eaaa90099b6eb96a5730619ca2df08f.png)
(2)当
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e464598d8d334b4d5a01c25f7ef9021c.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/081fad2749f3f201cf2c324c3d0dd190.png)
(3)令
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/971ea1d21d48c4e9a02f633eaada730f.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/38fcec7af3520884b173b29bda6c657a.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/13d85d20b743e236a83edb22d5229d05.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f13d06dcfd70149e4f495614f36b3a72.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/f44b482719577dde6fa146e44aa0c448.png)
![](https://staticzujuan.xkw.com/quesimg/Upload/formula/e6291d7b91f71daa0b3c4fa02dc7a5ea.png)
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