2026 AMC 8 第 22 题

先试着解答 2026 AMC 8 第 22 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 2026 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.

将整数 11 到 2525 任意分成五组,每组 55 个数。找出每组的中位数,再在这五个中位数中取中位数,记为 MM。MM 的最小可能值是多少?
The integers from 11 through 2525 are arbitrarily separated into five groups of 55 numbers each. The median of each group is identified. Let MM equal the median of the five medians. What is the least possible value of M?M?
99
1010
1212
1313
1414
答案:A
知识点:中位数(数据)抽屉原理极端原理
小提示:
一个五个数的组中位数不超过 mm,至少需要该组有 33 个数不超过 mm。
A group median at most mm needs at least 33 numbers at most mm
大提示:
若想让五个中位数的中位数很小,就需要至少三组都有较小的中位数。
Three small medians would require too many small numbers
视频讲解:
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文字解答:
如果某组的中位数至多为 88,那么这一组至少有 33 个数不超过 88。若五个中位数的中位数至多为 88,则至少有 33 组满足这一点,需要至少 99 个不超过 88 的数,矛盾。因此 M≥9M\ge9。这个下界可以达到,例如让五组的中位数为 5,8,9,12,175,8,9,12,17:{3,4,5,20,21}\{3,4,5,20,21\}、{6,7,8,22,23}\{6,7,8,22,23\}、{1,2,9,24,25}\{1,2,9,24,25\}、{10,11,12,13,14}\{10,11,12,13,14\} 和 {15,16,17,18,19}\{15,16,17,18,19\}。所以最小值是 99。
If a group has median at most 88, then at least 33 numbers in that group are at most 88. For the median of the five medians to be at most 88, at least 33 groups would need such medians, requiring at least 99 numbers at most 88, impossible. Thus M≥9M\ge9. This is attainable, for example with group medians 5,8,9,12,175,8,9,12,17: use groups {3,4,5,20,21}\{3,4,5,20,21\}, {6,7,8,22,23}\{6,7,8,22,23\}, {1,2,9,24,25}\{1,2,9,24,25\}, {10,11,12,13,14}\{10,11,12,13,14\}, and {15,16,17,18,19}\{15,16,17,18,19\}. Hence the least possible value is 99.
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