finding the mean on frequency charts

can you explain how to find the mean of a frequency chart using (x f and fx) with three colums in a chil friendly way !

If the data is grouped into certain intervals e.g. 0-10, 11-20, 21-30 etc then the first column you need (after the one that tells you the frequency (f)) is one that tells you the midpoints (x) of these groups e.g 5, 15, 25 etc. You then multiply this midpoint by the frequency fx. For example if your midpoint is 5 for the 0-10 interval and the number of times this occurs is 4 you would multiply 5x4 to get 20. You then stick this answer in your final column. When you've calculated all the fx for all the intervals you add them all up and then divide by the total number of bits of data in the table (i.e. the total frequency) Simple.
01 March 2011
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