I just took 15 practice questions for the bar exam and I missed all 15 (don't worry for me, this question set was on a subject I have yet to learn ). This made my chuckle becuase I thought it was pretty unlikely. There are four answer choices for each question. I know that on average I should at least answer 3.75 correctly. (.25 x 15). But at the outset, what was the probability that I would miss all 15? in other words, if there is a 25% chance of an event occuring over 15 occurrences and that event never occurs, what is the probability? I'm not sure what the formula is.