2020 AMC 10B Problem 11


Ms. Carr asks her students to read any 55 of the 1010 books on a reading list. Harold randomly selects 55 books from this list, and Betty does the same. What is the probability that there are exactly 22 books that they both select?

(A) 18(B) 536(C) 1445(D) 2563(E) 12\textbf{(A)}\ \frac{1}{8} \qquad\textbf{(B)}\ \frac{5}{36} \qquad\textbf{(C)}\ \frac{14}{45} \qquad\textbf{(D)}\ \frac{25}{63} \qquad\textbf{(E)}\ \frac{1}{2}


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

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Problem Tags: Counting and probability

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Category: AMC 10B
Points: 3
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