1到1000有多少个9

20*9+120=300
1到99共20个9 100到199
200到299 300到399 400到499 500到599 600到699 700到799 800到899
都是20个9
所以1到899
一共20*9个9
900 999 百位上的9共100个 十位上的9共10个 个位上的9共10个
一共120个9

所以1到1000共
20*9+120=300个9

一共有209个9.

……无数个，谢谢啊

90吧

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