1991 AMC 8 第 24 题

先试着解答 1991 AMC 8 第 24 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。

24.

一个边长为 33 厘米的正方体被切成 NN 个较小的正方体,且这些小正方体不全同样大小。如果每个小正方体的边长都是整厘米数,那么 N=N =
A cube of edge 33 cm is cut into NN smaller cubes, not all the same size. If the edge of each of the smaller cubes is a whole number of centimeters, then N=N =
44
88
1212
1616
2020
答案:E
知识点:正方体体积
小提示:
小正方体的边长必须是整数,所以只能是边长 11 或边长 22
The smaller cubes must have whole-number edges, so each is edge 11 or edge 22
大提示:
只能放下一个边长为 22 的正方体;剩下的体积 27−827 - 8 用单位正方体填满
Only one edge-22 cube fits; the rest are unit cubes filling the remaining volume 27−827 - 8
解答:
这个 3×3×33 \times 3 \times 3 正方体的体积是 2727。由于小正方体更小且边长为整数,它们的边长只能是 11 或 22。原正方体内不能放下两个互不相交的边长为 22 的正方体,因为要将它们分开,某个方向上的总跨度至少为 44。因此最多只能放下一个边长为 22 的正方体。
剩余体积 27−8=1927 - 8 = 19,由 1919 个单位正方体填满。总数是 1+19=201 + 19 = 20 个正方体。
所以正确答案是 E。
The 3×3×33 \times 3 \times 3 cube has volume 27.27. Since the cubes are smaller and have whole-number edge lengths, their edges are 11 or 22. Two edge-22 cubes cannot be disjoint inside the original cube: separating them would require a total span of at least 44 in some direction. Thus at most one edge-22 cube fits.
The remaining 27−8=1927 - 8 = 19 of volume is filled by 1919 unit cubes. That is 1+19=201 + 19 = 20 cubes.
Thus, the correct answer is E .
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