AMC 8 1985 Problem 22

AMC8 1985 年第 22 题

概率★★★★☆

Assume every 7-digit whole number is a possible telephone number except those that begin with 0 or $1$. What fraction of telephone numbers begin with 9 and end with 0?

假设除了以 0 或 1 开头的号码外，所有七位正整数都是可能的电话号码。以 9 开头且以 0 结尾的电话号码占几分之几？

A. $\displaystyle \frac{1}{63}$
B. $\displaystyle \frac{1}{80}$
C. $\displaystyle \frac{1}{81}$
D. $\displaystyle \frac{1}{90}$
E. $\displaystyle \frac{1}{100}$

正确答案 · Correct Answer

B

解析 · Solution

解析整理中

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