1985 AMC 12 第 9 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。
9.
正奇数 、、、、 按图示规律排列成五列并继续延伸。从左数， 所在的列是第几列？
The odd positive integers, are arranged in five columns continuing with the pattern shown. Counting from the left, the column in which appears is the
第一列
first
第二列
second
第三列
third
第四列
fourth
第五列
fifth
小提示：
观察每个从左向右排列的行的首项
Look at the entries that begin each left-to-right row
大提示：
将 与附近的 的倍数联系起来
Relate to a nearby multiple of
解答：
每个从右向左排列的行的末项为 ，下一行从第二列的 开始。由于 ，它是这样一行的首项，位于第二列。
所以正确答案是 B。
The last number in each right-to-left row is and the next row begins with in the second column. Since it begins such a row and lies in the second column.
Thus the correct answer is B.
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