AMC 10 Step by Step
2010 AMC 10AProblem 23P21-25~5 minPrint

Each of 2010 boxes in a line contains a single red marble, and for 1k20101 \le k \le 2010 , the box in the kthk\text{th} position also contains kk white marbles. Isabella begins at the first box and successively draws a single marble at random from each box, in order. She stops when she first draws a red marble. Let P(n)P(n) be the probability that Isabella stops after drawing exactly nn marbles. What is the smallest value of nn for which P(n)<12010P(n) < \frac{1}{2010} ?

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Problem © Mathematical Association of America (MAA), American Mathematics Competitions. Reproduced for non-commercial educational use. Solution and commentary are original to this site.