B*V
发帖数: 3365 | 1 【 以下文字转载自 Medicalpractice 讨论区 】
发信人: ChiUSMD (治病治病), 信区: Medicalpractice
标 题: 美国中学数学
发信站: BBS 未名空间站 (Sat Feb 11 14:23:52 2012, 美东)
过去听人说，美国中学生不学数学。上次见九年级儿子数学考卷，操，真tnnd难。那不
是奥数，就中考。包子求解。
A 3x3 square is partitioned into 9 unit square, each square is painted
either white or black with each color being equally likely, randomly. The
square is then rotated 90 degree, and every white square in a position
formerly occupied by a black square is painted black. The color of all other
squares are left unchanged. What is the probability that the grid is now
entirely black. |
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