2024 AMC 8 第 16 题
先试着解答 2024 AMC 8 第 16 题,然后核对你的答案与视频与精心整理的解答,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 2024 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。
16.
Minh 把 到 的数字以某种顺序填入一个 网格。她计算每一行和每一列中数字的乘积。最少有多少行和列的乘积能被 整除?
Minh enters the numbers through into the cells of a grid in some order. She calculates the product of the numbers in each row and column. What is the least number of rows and columns that could have a product divisible by
答案:D
视频讲解:
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文字解答:
从 到 共有 个 的倍数。一行或一列的乘积能被 整除,当且仅当它至少含有一个这样的倍数。
设有 行和 列的乘积能被 整除。所有 的倍数都必须位于这些 行与 列的交叉格中,所以 个倍数必须装入 个格子。若 ,则 ,格子不够。因此至少要标记 行和列。
可以把 个 的倍数放入一个 区块,再把剩下的 个放在这些行中的第六列。这样恰好标记 行和 列,共 。
正确答案是 D。
There are multiples of from through . A row or column has product divisible by exactly when it contains at least one of these multiples.
Suppose rows and columns have products divisible by . Every multiple of must lie in one of those rows and also in one of those columns, or else it would create another marked row or column. Thus the multiples must fit in the intersection cells. If , then , which is too small. So at least rows and columns are needed.
This can be done by placing multiples of in a block, then placing the remaining multiples in a sixth column within two of those same rows. Then exactly rows and columns are marked, for a total of .
Thus, D is the correct answer.
其他年份的第 16 题
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