Assume your friend just took an exam made up of 20 true/false questions. Further assume that your friend had no knowledge relevant to the questions, and consequently just guessed the answer to each question What is the probability your friend will pass the exam. Each question has the same weight and 60% or more correct answers results in a passing grade.
A) 0.1316
B) 0.1307
C) 0.2517
D) 0.0580

Question

Quizplus · Accepted Answer

The probability of guessing the correct answer to a true/false question is 0.5. Since all questions are equally weighted, the probability of guessing the correct answer to all 20 questions is (0.5)^20, which is approximately 0.00095. The probability of guessing at least 12 questions correctly (to get a passing grade of 60% or higher) can be computed using a binomial distribution with n=20 and p=0.5. Using a calculator or spreadsheet, we find that this probability is approximately 0.2517 or 25.17%. Therefore, the probability of passing the exam through guessing is 0.2517, which corresponds to choice C.

Assume Your Friend Just Took an Exam Made Up of 20