1987 AMC 8 第 18 题
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所有题目均经美国数学协会（MAA）官方合法授权使用。
18.
房间里一半的人离开了。剩下的人中有三分之一开始跳舞。此时有 人没有跳舞。房间里原来有多少人？
Half the people in a room left. One third of those remaining started to dance. There were then people who were not dancing. What was the original number of people in the room?
小提示：
一半人离开后，剩下的人数才是跳舞比例所作用的总数
After half leave, the number remaining is what the dancing fraction applies to
大提示：
个没跳舞的人是剩余人数的
The non-dancers are of those remaining
解答：
在留下的人中， 跳舞，所以 没跳舞。因此剩余人数的 等于 ，得剩余 人。
这 人是原来人数的一半，所以房间一开始有 人。
所以正确答案是 C。
Of those remaining, danced, so did not. Thus of the remaining people equals giving remaining.
Those are half the original group, so the room started with people.
Thus, the correct answer is C .
其他年份的第 18 题
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