A quiz consists of 7 multiple choice questions, each with 4 possible answers. To pass the quiz, it is you must get at least 3 questions correct. An unprepared student can do nothing except guess answers at random. What is the probability that the student passes?
I'm thinking you use the distributive property which gives you ${7 \choose 3} (0.25)^3 (0.75)^4$ but I'm not sure where to go from here.