2012 AMC 8 第 9 题
先试着解答 2012 AMC 8 第 9 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 2012 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。
9.
Fort Worth Zoo 有一些两条腿的鸟和一些四条腿的哺乳动物。Margie 某次参观动物园时数到 个头和 条腿。Margie 数到的动物中有多少是两条腿的鸟？
The Fort Worth Zoo has a number of two-legged birds and a number of four-legged mammals. On one visit to the zoo, Margie counted heads and legs. How many of the animals that Margie counted were two-legged birds?
答案：C
小提示：
先假设每只动物都有两条腿。
Start by giving every animal two legs.
大提示：
多出来的腿决定四条腿哺乳动物的数量。
The extra legs determine the number of four-legged mammals.
视频讲解：
Click to load, then click again to play
文字解答：
设 为 条腿动物的数量， 为 条腿动物的数量。
数腿得到 ，数头得到 。将第二式乘以四，得 。减去第一式，得到 。因此有 只两条腿的鸟。
所以正确答案是 C。
Let be the number of animals with legs and let be the number of animals with legs.
Counting the number of legs yields and counting the number of heads yields This means and subtracting the first equation from the second yields This means there are two-legged birds.
Thus, the answer is C .
其他年份的第 9 题
- 1985 AMC 8
- 1986 AMC 8
- 1987 AMC 8
- 1988 AMC 8
- 1989 AMC 8
- 1990 AMC 8
- 1991 AMC 8
- 1992 AMC 8
- 1993 AMC 8
- 1994 AMC 8
- 1995 AMC 8
- 1996 AMC 8
- 1997 AMC 8
- 1998 AMC 8
- 1999 AMC 8
- 2000 AMC 8
- 2001 AMC 8
- 2002 AMC 8
- 2003 AMC 8
- 2004 AMC 8
- 2005 AMC 8
- 2006 AMC 8
- 2007 AMC 8
- 2008 AMC 8
- 2009 AMC 8
- 2010 AMC 8
- 2011 AMC 8
- 2013 AMC 8
- 2014 AMC 8
- 2015 AMC 8
- 2016 AMC 8
- 2017 AMC 8
- 2018 AMC 8
- 2019 AMC 8
- 2020 AMC 8
- 2022 AMC 8
- 2023 AMC 8
- 2024 AMC 8
- 2025 AMC 8
- 2026 AMC 8