1991 AMC 8 第 22 题
先试着解答 1991 AMC 8 第 22 题，然后核对你的答案与精心整理的解答，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 1991 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。
22.
每个转盘都被平均分成 部分。转动两个转盘，把得到的两个数相乘。乘积为偶数的概率是多少？
Each spinner is divided into equal parts. The results obtained from spinning the two spinners are multiplied. What is the probability that this product is an even number?
小提示：
乘积只有在两个数都是奇数时才是奇数；除此以外都是偶数
A product is even unless both spun numbers are odd
大提示：
先求奇数乘积的概率，也就是奇数乘奇数，再用 减去它
Find the probability of an odd product (odd times odd), then subtract from
解答：
乘积为奇数当且仅当两个数都是奇数。第一个转盘转到奇数 或 的概率是 ，第二个转盘转到奇数 的概率是 。
所以乘积为奇数的概率是 ，乘积为偶数的概率是 。
所以正确答案是 D。
The product is odd only when both numbers are odd. The first spinner is odd ( or ) with probability and the second is odd () with probability
So the product is odd with probability and even with probability
Thus, the correct answer is D .
其他年份的第 22 题
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