1993 AMC 8 第 25 题
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25.
一个棋盘由边长为一英寸的正方形组成。一张边长为 英寸的正方形卡片放在棋盘上,使它覆盖了 个小正方形的部分或全部面积。 的最大可能值是
A checkerboard consists of one-inch squares. A square card, inches on a side, is placed on the board so that it covers part or all of the area of each of squares. The maximum possible value of is
或
or
或
or
或
or
或
or
或更多
or more
答案:E
解答:
将卡片旋转 ,并把中心放在四个棋盘小格相交的角点上。因为卡片对角线 大于 ,卡片的四个角都会越过网格线伸入下一格。
卡片覆盖中央的 共 个小正方形,并且在四边各伸入另外 个小正方形,总共 个。
这也是最大可能值。卡片边长只有 英寸,所以水平和竖直方向跨度都最多约 英寸,因此它位于一个 、共含 格的方格块内。只有卡片的四个尖角能到达该方格块边缘,它不可能到达这个方格块的四个角格,所以最多覆盖 个。既然 可以达到,最大值就是 ,属于“ 或更多”。
所以正确答案是 E。
Tilt the card and center it on a corner where four grid squares meet, as shown. Because the card's diagonal, is longer than each of the four corners of the card reaches past a grid line into the next square.
The card covers the central block of squares and pokes into more squares on each of its four sides, giving squares.
This is also the most possible. The card is only inches wide, so its overall width and height are each at most inches; it therefore lies within a block of squares. Its four pointed corners are the only parts that reach the edge of that block, so it can never reach the four corner squares of the block, leaving at most Since is achievable, the maximum is which falls in the range " or more."
Thus, the correct answer is E .
其他年份的第 25 题
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