During a five day period, Laurel served a different number of customers at her saloon each day. The mean number of daily customers served during this period was 20. In the following month, during the same five-day period, she served 15 customers for four of the days, but in the fifth day she served 60 customers. What is the difference between the means of number of customers she served during the two five-day periods?

It depends on the subject for me. some exams are easier than others so i usually go through it and answer questions i know based on my general knowledge, then double check after. going through the lesson can a lot  because the exams can be  very lesson-specific, but sometimes they are ridiculously long so a lot of people don't take the time. i did find that, when i went through the lessons, i was making 100's on my exams vs strictly using + the internet and  i make 90's.