Stack of Crates
Source: AIME 2008I Problem 9
March 23, 2008
probabilityfunctionalgebrapolynomialnumber theoryrelatively primegeometric series
Problem Statement
Ten identical crates each of dimensions ft ft ft. The first crate is placed flat on the floor. Each of the remaining nine crates is placed, in turn, flat on top of the previous crate, and the orientation of each crate is chosen at random. Let be the probability that the stack of crates is exactly ft tall, where and are relatively prime positive integers. Find .