2000 AMC 8 第 12 题

先试着解答 2000 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 2000 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.

要建造一面长 100100 英尺、高 77 英尺的砌块墙,使用的砌块高 11 英尺,长度可以是 22 英尺或 11 英尺(不得切割砌块)。砌块的竖缝必须如图所示错开,且墙两端必须齐平。建造这面墙最少需要多少块砌块?
A block wall 100100 feet long and 77 feet high will be constructed using blocks that are 11 foot high and either 22 feet long or 11 foot long (no blocks may be cut). The vertical joins in the blocks must be staggered as shown, and the wall must be even on the ends. What is the smallest number of blocks needed to build this wall?
344344
347347
350350
353353
356356
答案:D
知识点:最优化
小提示:
从全部使用 22 英尺砌块开始考虑。
Start with all 22-foot blocks
大提示:
为了错开竖缝,只需每隔一行多用砌块。
Only every other row needs an extra block to stagger joins
解答:
墙共有 77 行,每行高 11 英尺。
为了使用最少砌块,第 11、33、55 和 77 行可采用图中底行的模式,每行需要 5050 块砌块。
第 22、44 和 66 行采用图中上行的模式,中间有 4949 块 22 英尺砌块,两端各有一块 11 英尺砌块,共 5151 块砌块。
将 44 行 5050 块和 33 行 5151 块相加,得到 4⋅50+3⋅51=200+153=3534 \cdot 50 + 3 \cdot 51 = 200 + 153 = 353 块砌块。
所以正确答案是 D。
The total number of rows in the wall is 7,7, with each row being 11 foot high.
To use the minimum number of bricks, rows 1,1, 3,3, 5,5, and 77 will have the same pattern as the bottom row in the picture, which requires 5050 bricks to construct.
Rows 2,2, 4,4, and 66 will have the same pattern as the upper row in the picture, which has 4949 22-foot bricks in the middle and one 11-foot brick on each end, for a total of 5151 bricks.
When you add up 44 rows of 5050 bricks and 33 rows of 5151 bricks, you get a total of 4⋅50+3⋅51=200+153=3534 \cdot 50 + 3 \cdot 51 = 200 + 153 = 353 bricks.
Thus, D is the correct answer.
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