Diana took a multiple-choice test of 50 questions and each question carried two marks. The probability that Diana chose the correct answer for a question was three out of four. The marks for grade A, grade B and grade C were 80, 72 and 64, respectively. After the test, Diana was told by her tutor that she did not get grade A. Using normal approximation of the binomial distribution, find the probability that she got grade C?
Does the formla in this case is P(C grade | no A grade) = P(64<= x < 72 | X<80)?
I think it will be something like this, but do binomial distribution support it? or I need to break down into two formlas like find out P(C and B grade | no A grade) then find out P(C grade | C and B grade)?