1994 AMC 8 第 12 题

先试着解答 1994 AMC 8 第 12 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 1994 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。

12.

图中的三个大正方形大小相同。各线段与正方形边的交点都是边的中点。三个正方形中的阴影面积如何比较?
Each of the three large squares shown is the same size. Segments that intersect the sides of the squares intersect at the midpoints of the sides. How do the shaded areas of these squares compare?
三个阴影面积都相等。
The shaded areas in all three are equal.
只有 II 和 IIII 的阴影面积相等。
Only the shaded areas of II and IIII are equal.
只有 II 和 IIIIII 的阴影面积相等。
Only the shaded areas of II and IIIIII are equal.
只有 IIII 和 IIIIII 的阴影面积相等。
Only the shaded areas of IIII and IIIIII are equal.
II、IIII 和 IIIIII 的阴影面积都不同。
The shaded areas of I,I, II,II, and IIIIII are all different.
答案:A
知识点:面积分割面积比
小提示:
把每个图形切成若干相等小块,求每个大正方形中阴影部分所占的比例
Find what fraction of each large square is shaded by cutting each figure into equal smaller pieces.
大提示:
把正方形 II 分成 88 个相等三角形,正方形 IIII 分成 44 个相等小格,正方形 IIIIII 分成 1616 个相等三角形,再数阴影块数
Divide square II into 88 equal triangles, square IIII into 44 equal cells, and square IIIIII into 1616 equal triangles, then count the shaded pieces in each.
解答:
在正方形 IIII 中,阴影占 11 个小格,总共有 44 个相等小格,所以阴影面积是 14\tfrac14。
正方形 II 可分成 88 个相等三角形,其中 22 个涂色;正方形 IIIIII 可分成 1616 个相等三角形,其中 44 个涂色。这些比例都是 28=416=14\tfrac{2}{8} = \tfrac{4}{16} = \tfrac14。
因为三个图形的阴影面积都占 14\tfrac14,所以阴影面积全都相等。
所以正确答案是 A。
In square II,II, 11 of the 44 equal cells is shaded, so 14\tfrac14 of it is shaded.
Square II breaks into 88 equal triangles with 22 shaded, and square IIIIII breaks into 1616 equal triangles with 44 shaded; each of these equals 28=416=14.\tfrac{2}{8} = \tfrac{4}{16} = \tfrac14.
Since every figure has exactly 14\tfrac14 shaded, the shaded areas are all equal.
Thus, the correct answer is A .
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