MathDB
2021 LMT Spring Division A Problem 10

Source:

October 22, 2021

Problem Statement

Pieck the Frog hops on Pascal's Triangle, where she starts at the number 11 at the top. In a hop, Pieck can hop to one of the two numbers directly below the number she is currently on with equal probability. Given that the expected value of the number she is on after 77 hops is mn\frac{m}{n}, where mm and nn are relatively prime positive integers, find m+nm+n.
Proposed by Steven Yu