A quiz consists of 100 multiple choice questions, each with five possible answers, only one of which is correct. If the student guesses on each question, what is the probability that student answered at least 30 questions correctly.
answer = 0.087
What I tried:
I used the binomial CDF formula
I tried doing the 1 - bionomial CDF of n = 100, p = 0.2 and x = 30, so
$p(x>=30) =1-p(x<30)= 1-binoCDF(100,0.2,29) = 0.0112$
but as you can see that's not right.