1962 AMC 12 第 20 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。
20.
一个五边形的五个内角成等差数列。其中必有一个角的度数为：
The angles of a pentagon are in arithmetic progression. One of the angles, in degrees, must be:
小提示：
五个成等差数列的数，其中间项等于这五项的平均数
Five terms in arithmetic progression have their middle term equal to their average
大提示：
五边形的内角和为
The interior angles of a pentagon sum to
解答：
五个角的平均数为 。对于五个成等差数列的数，中间项等于平均数，所以必有一个角为 。
所以正确答案是 A。
The average of the five angles is For five terms in arithmetic progression, the middle term equals the average, so one angle must be
Thus, the correct answer is A.
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