1. The problem statement, all variables and given/known data While shooting at target, soldier shoots from machine gun fixed in a way so it can rotate only around z axis. deviation from center of target due to twitching of machine gun is random variable with Gauss distribution. Deviations are such that inside of 20m from center of target, it hits 80% bullets. Find the distance, at how long away from center of target does 50% of the bullets end up. 3. The attempt at a solution Since I'm dealing with gauss distribution, I must find σ and μ . My problem is next. Idea is to integrate some parts and then i get numbers in table. But what bothers me is next, what does 20 m and unknown distance represents? What is σ and μ in this very problem?