Question

Assume that random guesses are made for thirteen multiple choice questions on a medical admissions test, so that there are n 13 trials, each with a probability of success (correct) given by p 0.20. Find the probability that the number x of correct answers is fewer than 5. The probability that the number x of correct answers is fewer than 5 is (Round to three decimal places as needed.)

Answer 1

Let X follow a binomial distribution with parameters (n=13,p=0.20)

we want p(X<5)

pbinom(q = 4,size=13,prob = 0.20,lower.tail = TRUE) = 0.9008694