I cannot figure out what formula to use for the following questions. If a student is taking a ten question (four answer choices per question) how do you figure out the probability of:
a) getting at least one question rcorrect
b)passing the exam (at least 6 correct)
c) getting an A (at least 9 correct)
I have tried several and none seems to produce the correct answers. I have been working on this (and another question that I cannot even begin to explain) for a couple of days. Any help would be greatly appreciated.