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For more information, please see full course syllabus of SAT: Mathematics

For more information, please see full course syllabus of SAT: Mathematics

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Post by Jeffrey Tao on October 26, 2013

This is more of an important point for other viewers than a question. In the case of the crayons, the probability of picking in the AND case is 1/10 x 1/10 ONLY if after one crayon is picked, it is put back into the box before the second pick. Otherwise, if the crayon is left out, the probability is 1/10 x 1/NINE because if the crayon isn't put back after the first draw, then during the second time picking the crayon, there will be only nine crayons, thus it is 1/NINE x 1/10.