The first thing the researcher wants to do is sort their ages. In the US, high school students probably fall within grades 9-12 or 10-12. While middle school students between grade one and six. This is a grouped data; to find the mean, we have to take cognizance of the "how many" I.e frequency; the mean of high school students is the sum of the product of the frequencies of their Age brackets multiplied by the midpoint of each age bracket divided by the sum of their frequencies. Say we have 12-14 yrs (where midpoint is 13 that is ((12 +14)/2) and this group say they watch 9 times then we multiply the midpoint and divide by the sum of the frequencies. If we do same for the middle school students, we can take the difference.
