There are 100 questions from a SAT test, and they are all multiple choice with possible answers of a,b,c,d,e for each question only one answer is correct. Find the mean number of correct answers for those who make random guesses for all 100 questions?
1/5 * 100 = 20
To find the mean number of correct answers for those who make random guesses on all 100 questions, we need to calculate the probability of getting each question correct and then multiply it by the total number of questions.
Since there are 5 possible answers (a, b, c, d, e) for each question and only one answer is correct, the probability of guessing the correct answer for each question is 1/5, or 0.2.
Now, let's calculate the number of correct answers that are expected by multiplying the probability of getting each question correct (0.2) by the total number of questions (100):
mean number of correct answers = probability of getting each question correct * total number of questions
= 0.2 * 100
= 20
Therefore, the mean number of correct answers for those who make random guesses on all 100 questions is 20.