text: let say i have 5 tests marks of 30 students..? let say i have 5 tests marks of 30 students, and i plot them in a graph of 30 lines. what must i do to get 1 line that can summarize the pattern of the marks?  do i take the mean of all the 30 students, or what?  what distribution would this be u think? normal?  really need opinion on this...thanks there is such a thing as a matrix plot, which is a way to display all possible two-way scatter plots (in this case, it's 5!/(2!3!) = 10 different scatter plots).  i posted a link below to see what a matrix plot looks like.  of course you really can't see a normal distribution on a scatter plot.  if you add up the students exams or take the mean, you can draw a histogram of the data to get an idea what the distribution looks like.  it's possible that they are normally distributed, but it depends on the exams and the skill level of the class.  if one exam is easy, then its distribution would be skewed to the left (meaning it has a left tail), which would not be normal-looking.  same thing with hard exams except those would be skewed to the right.  then also, since classes are not selected randomly and the tests are different, you cannot be assured that the central limit theorem will hold for the means, especially since you are only taking the means of 5 tests, but it is possible that you will.