2010 AMC 12A Problem 19


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} ?

(A) 45(B) 63(C) 64(D) 201(E) 1005\textbf{(A)}\ 45 \qquad \textbf{(B)}\ 63 \qquad \textbf{(C)}\ 64 \qquad \textbf{(D)}\ 201 \qquad \textbf{(E)}\ 1005


Full credit goes to MAA for authoring these problems. These problems were taken on the AOPS website.

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Category: AMC 12A
Points: 3
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