1. The problem statement, all variables and given/known data Roll a fair die until the first time you roll a '5' then stop. Let X be the number of times you rolled the die. What is the probability that X is divisible by 3? 2. Relevant equations E[X] ? 3. The attempt at a solution I honestly have no idea how to even approach this sort of thing. My first thought was either a bionomial or geometric series, but that could possibly be endless. any sort of hints or suggestions would be great.