Group A includes 20 students who took an exam and their grade mean was 28(±9.15).
After taking the second exam, their mean grade has decreased by 14(±9.9) in comparison with the first exam.
My question is: How to find the average score of their second exam if it not given?
I know that I can subtract the averages and get an estimate of their second exam average. However, I would like to know how to get the most accurate average, and whether the SD has any use in this process.