On a multiple-choice test, the chance of randomly guessing the correct answers to a question is 25%. If you guess the answer to every question on a 20-question test, how many should you expect to get correct?
Since there are four possible answers to each question and only one is correct, the probability of guessing the correct answer is 1/4 or 25%.
If you guess on each of the 20 questions, you can expect to get 20 x 0.25 = 5 questions correct on average.
Therefore, you should expect to get 5 questions correct by guessing on a 20-question multiple-choice test.