# Thread: Discrete Probability Distributions

1. ## Discrete Probability Distributions

A multiple-choice examination has 15 questions. Each question has four possible answers of which only one is correct. The probability that by just guessing a student will get exactly 7 correct is?

2. ${15 \choose 7}(s)^7(1-s)^{15-7}$
Where $s$ is the probability of success.

3. Thanks, and I assume that s would be 0.25 because of four possible choices and one correct answer.