1990 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.
一个长方体的每个顶点都被一刀切掉，切面穿过该顶点相邻的三条棱，在八个顶点各切去一个小三角形部分。新立体有多少条棱？
Every corner of a rectangular prism is cut off by a straight slice through the three edges meeting at that corner, removing a small triangular piece at each of the eight corners. How many edges does the new figure have?
答案：C
小提示：
原来的长方体有 条棱，而且这些棱不会完全消失
The original rectangular prism has edges, and none of them disappear
大提示：
每切掉一个顶点都会产生一个新的三角形面，增加 条新棱
Each corner cut creates a new triangular face, adding new edges
解答：
长方体原来有 条棱。切掉顶点只会把这些棱截短，不会把它们完全去掉。
共有 个顶点，每个顶点切口会产生一个小三角形面，带来 条新棱。所以新增 条棱，总数是 。
所以正确答案是 C。
A rectangular prism starts with edges, and cutting corners only shortens them without removing any.
Each of the corner cuts creates a small triangular face with new edges, adding edges. The total is .
Thus, the correct answer is C .
其他年份的第 18 题
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