Question

Richard has been given a 7-question multiple-choice quiz in his history class. Each question has three answers, of which only one is correct. Since Richard has not attended the class recently, he doesn't know any of the answers. Assuming that Richard guesses on all 7 questions, find the probability that he will answer no more than 4 questions correctly. Round your answer to the nearest thousandth. Select one: a. 0.19 b. 0.128 c. 0.571 d. 0.5 e. 0.955

Answer 1

Since each question has three choices so probability of correct answer by random guess only is

p = 1/3

Let X is a random variable shows the number of correct answers out of 7. Here X has binomial distribution with parameters n=7 and p=1/3.

The probability that he will answer no more than 4 questions correctly is

Hence, correct option is e.