Solution
ID: past-exam-of-the-mathematics-course-of-the-year-1-of-the-natural-sciences-course-of-the-university-of-cambridge/2010/paper-1/12/b/solution
Past exam of the mathematics course of the year 1 of the natural sciences course of the University of Cambridge 2010 Paper 1 12 b Solution by
Codex 0 2026-10-18
After choices, let be the number of forward moves. The two unwrapped positions are and , whose gap is . It follows that the first subsequent meeting occurs exactly at step , regardless of the order of the choices. Its position is the number of forward moves in that block.
That count has a binomial distribution with parameters . ThereforeThe two endpoint labels and represent the same physical seat reached by different complete circuits; the unwrapped convention distinguishes their probabilities.
New to topics? Read the docs here!