1. The problem statement, all variables and given/known data 2. Relevant equations f(x) = e-λλx/x! 3. The attempt at a solution Initially I thought I could solve this problem using the Law of Memoryless. That, the solution would just be P(X <= 2). However, I was wrong. Turns out the solution is P(X <= 4.5) - P(X<= 2.5). Does anyone know why?