2019 AMC 8 第 15 题
先试着解答 2019 AMC 8 第 15 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 2019 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。
15.
海滩上有 人戴太阳镜， 人戴帽子。有些人两者都戴。如果从戴帽子的人中随机选一人，此人也戴太阳镜的概率是 。如果改为从戴太阳镜的人中随机选一人，此人也戴帽子的概率是多少？
On a beach people are wearing sunglasses and people are wearing caps. Some people are wearing both sunglasses and caps. If one of the people wearing a cap is selected at random, the probability that this person is also wearing sunglasses is If instead, someone wearing sunglasses is selected at random, what is the probability that this person is also wearing a cap?
答案：B
小提示：
用戴帽子的人群先求两者都戴的人数
Use the cap group to find the number wearing both
大提示：
再把同一个交集人数除以戴太阳镜的人数
Then divide that same overlap by the number wearing sunglasses
视频讲解：
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文字解答：
概率为 ，表示戴帽子的人中有 也戴太阳镜。
所以两者都戴的人数为 。
从戴太阳镜的五十人中随机选，选到也戴帽子的概率为 。
正确答案是 B。
If the probability is that means of the people wearing caps are also wearing sunglasses.
This means that people are wearing both caps and sunglasses.
The probability of a person wearing sunglasses also wearing a cap is
Thus, the correct answer is B.
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