How many number '9' are required to represent the numbers between 10 to 100?

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How many number '9' are required to represent the numbers between 10 to 100?

喂喂.楼上的你好好数一数好不.
问题翻译过来是问你如果想要把10到100之间所有数写出来需要多少个9.
19,29,39,49,59,69,79,89,90,91,92,93,94,95,96,97,98,99
这一共是19个啊. 99是两个9.

19,29,39,49,59,69,79,89,90,91,92,93,94,95,96,97,98,99
所以应该是18 个