Question

从 $1000$ 到 $9999$ 之间，有多少个四位整数的四个数字互不相同？

How many integers between $1000$ and $9999$ have four distinct digits?

$3024$

$4536$

$5040$

$6480$

$6561$

答案：B

知识点：乘法原理数字

难度评级：1070

视频讲解：

Click to load, then click again to play

文字解答：

首先，千位有 $9$ 种选择，因为 $0$ 不能选。

接着，百位有 $9$ 种选择，十位有 $8$ 种选择，个位有 $7$ 种选择。因此这样的整数共有 $9\cdot9\cdot8\cdot7 = 4536$ 个。

所以正确答案是 B。

First, there are $9$ digits to choose for the thousands digit since $0$ can't be chosen.

Then, after that, there are $9$ ways to choose the hundreds digit, $8$ ways to choose the tens digit, and $7$ ways to choose the ones digit. Therefore, we get $9\cdot9\cdot8\cdot7 = 4536$ ways to choose such an integer.

Thus, the correct answer is B .

2015 AMC 8 第 10 题

答案：B

难度评级：1070

视频讲解：

文字解答：

其他年份的第 10 题