posted by Pat on .
Suppose that the mean score of an exam was 77 when taken 30 students took it on time with a standard deviation of 2. A makeup of the same exam is given to 6 students. The retakes averaged a score of 83 with a standard deviation of 2.9. What is the average of the test scores?
Mean = Σx/n
Σx = n * mean1 = 30 * 77 = 2310
Σx = n * mean2 = 6 * 83 = 498
total mean = (2310+498)/(30+6) = ?