Question

A student takes an exam containing 18 multiple choice questions. Each question has 5 chokes. If the student guesses, what is the probablity that he will get less than 9 but more than 6 questions right?

Answer 1

To find the probability of getting less than 9 but more than 6 questions right, use the binomial probability formula. Calculate the probabilities of getting exactly 7 and exactly 8 questions right, and then add them together.

Step-by-step explanation:

To find the probability that the student will get less than 9 but more than 6 questions right, we need to find the probability of getting exactly 7 or 8 questions right.

The probability of getting a question right by guessing is 1/5, and the probability of getting a question wrong is 4/5.

Using the binomial probability formula, we can calculate the probabilities of getting exactly 7 and exactly 8 questions right:

1. Probability of getting 7 questions right: C(18, 7) * (1/5)^7 * (4/5)^11
2. Probability of getting 8 questions right: C(18, 8) * (1/5)^8 * (4/5)^10

Finally, we add these two probabilities together to find the total probability.