2024 AMC 8 第 13 题
先试着解答 2024 AMC 8 第 13 题，然后核对你的答案与视频与精心整理的解答，解答来自 LIVE by Po-Shen Loh。你也可以参加完整限时模拟考试、查看全部 2024 AMC 8 解答，或核对答案。
所有题目均经美国数学协会（MAA）官方合法授权使用。
13.
Buzz Bunny 在一组台阶上每次跳一级，可以向上跳，也可以向下跳。Buzz 从地面开始，跳 次后又回到地面，共有多少种跳法？（例如，一种跳法是上、上、下、下、上、下。）
Buzz Bunny is hopping up and down a set of stairs, one step at a time. In how many ways can Buzz start on the ground, make a sequence of hops, and end up back on the ground? (For example, one sequence of hops is up-up-down-down-up-down.)
小提示：
序列必须有三次向上和三次向下
The sequence must have three up hops and three down hops
大提示：
在任何时刻，向下次数不能超过向上次数
Buzz can never have more down hops than up hops at any point
视频讲解：
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文字解答：
所有序列都必须以向上 开始、以向下 结束，并且在任何时刻，向下的次数都不能超过此前向上的次数。可行序列为 共有五种可行序列。
所以正确答案是 B。
We can deduce from the choices that it is possible to exhaust all possible cases for this problem. Note that all sequences must start with up and end with down , and that it should not be possible to go down more times than Buzz has gone up so far. Keeping this in mind, we can arrive at the following possible cases: which is a total of five possible sequences.
Thus, B is the correct answer.
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