MathDB
2022 Combo Div 2 P4

Source:

February 28, 2022
combinatorics

Problem Statement

Dilhan is running around a track for 1212 laps. If halfway through a lap, Dilhan has his phone on him, he has a 13\frac{1}{3} chance to drop it there. If Dilhan runs past his phone on the ground, he will attempt to pick it up with a 23\frac{2}{3} chance of success, and won't drop it for the rest of the lap. He starts with his phone at the start of the 5K, what is the chance he still has it when he finished the 5K?
Proposed by Zack Lee, Daniel Li, Dilhan Salgado