2003 AMC 8 第 13 题

先试着解答 2003 AMC 8 第 13 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 2003 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。

13.

十四个白色立方体拼成右图。这个立体的整个表面,包括底面,都被涂成红色。然后将这个立体拆成单个立方体。有多少个单个立方体恰好有四个面是红色的?
Fourteen white cubes are put together to form the figure on the right. The complete surface of the figure, including the bottom, is painted red. The figure is then separated into individual cubes. How many of the individual cubes have exactly four red faces?
44
66
88
1010
1212
答案:B
知识点:立体几何表面积
小提示:
一个小立方体恰好有四个涂色面,当且仅当它接触两个其他立方体
A cube has four painted faces exactly when it touches two other cubes.
大提示:
分别考虑顶部立方体、底部角落立方体和剩余立方体
Separate the top cubes, bottom corner cubes, and remaining cubes.
解答:
一个小立方体恰好有四个面被涂色,当且仅当它恰好与两个其他立方体相连。
44 个顶部立方体只接触一个其他立方体,所以它们有 55 个涂色面。44 个底部角落立方体接触三个其他立方体,所以它们有 33 个涂色面。
剩下的 14−4−4=614-4-4=6 个立方体各恰好接触两个其他立方体,所以它们恰好有四个涂色面。
所以正确答案是 B。
A cube has exactly four painted faces exactly when it is attached to exactly two other cubes.
The 44 top cubes touch only one other cube, so they have 55 painted faces. The 44 bottom corner cubes touch three other cubes, so they have 33 painted faces.
The remaining 14−4−4=614-4-4=6 cubes each touch exactly two other cubes, so they have exactly four painted faces.
Thus, B is the correct answer.
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