How do you calculate weighted grades?

Most of the time when you calculate an average you are calculating a weighted average without thinking too much about it. A weighted average of a group gives more weight to one in the group if it occurs more then once. For example; in a room full of people you have 3 ten yr olds, 5 eight yr olds and 1 six yr old. What is the average age of the group? To find a nonweighted average just add the three ages represented, without regard to how many, and divide by three; (10 + 8 + 6)/3 = 8. A weighted average takes into account how many of each age there are; (3x10 + 5x8 + 1x6)/9 = 8.4 . (notice you divide by total number of people not the number of ages represented as previously). You will also notice that the weighted average is the same thing as writing down each person's age and dividing by the number of people.