2024 AMC 8 第 21 题
先试着解答 2024 AMC 8 第 21 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。
21.
一群青蛙（称为一个军团）住在树上。青蛙在阴影中会变成绿色，在阳光下会变成黄色。最初绿色青蛙与黄色青蛙的比为 。后来 只绿色青蛙移到阳光处， 只黄色青蛙移到阴影处。现在比为 。现在绿色青蛙和黄色青蛙的数量相差多少？
A group of frogs (called an army) is living in a tree. A frog turns green when in the shade and turns yellow when in the sun. Initially, the ratio of green to yellow frogs was Then green frogs moved to the sunny side and yellow frogs moved to the shady side. Now the ratio is What is the difference between the number of green frogs and yellow frogs now?
小提示：
设最初黄色青蛙数为
Let the initial yellow count be
大提示：
移动后，绿色净增加 ，黄色净减少
After the moves, green changes by and yellow changes by
视频讲解：
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文字解答：
设最初绿色青蛙有 只，黄色青蛙有 只，则 。移动后有
把 代入 ，即可求出原来的黄色青蛙数 ：
因此最初黄色有 只，绿色有 只。移动后黄色有 只，绿色有 只，差为 。
所以正确答案是 E。
We can let be the number of green frogs and be the number of yellow frogs. Initially, we have . Then, after some frogs moved, we have the following proportion:
Substituting for will allow us to determine the number of yellow frogs originally ():
Hence, there were yellow frogs and green frogs initially. After some frogs moved, we now have yellow frogs and green frogs, giving us a difference of between the number of green and yellow frogs.
Thus, E is the correct answer.
其他年份的第 21 题
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