Question: On a multiple choice test with 9 questions, each question has four possible answers, one of which is correct. For students who guess at all answers, find the variance for the number of correct answers.
The formula to find the variance is: o= square root of (n x p x q)
My n is 9, P is .25, q is .75. I got 1.3 but that is the wrong answer. I am sure I got my values mixed up. What are the correct values?
The standard deviation is $$\sigma = \sqrt{npq},$$ but the variance is just $$\sigma^2 = npq.$$ So you took the square root without needing to.