Use binomial distribution

Question

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?

Answer 1

np = 37.5 and square root npq = 3.06

grade c means between 32 and 36 right answers, i.e. between .49 and 1.79 std deviations from the mean

You can look in the table, but I get probability .27

BTW, the grade levels you suggested seem like "dumbing down" to mw