1. The problem statement, all variables and given/known data Question: Find the number of trials needed to be 90% sure of at least three or more success, given that probability of one success is 0.2 2. Relevant equations N/A 3. The attempt at a solution My initial attempt at the problem was finding the probability of at least one success, then multiplying it by three, however that isn't the correct answer. I've found the answer via trial and error using binomial calculators online, but I still cannot seem to work it out by math. Is it even possible? or is it far too complicated to find the number of trials for something for least two or more successes?