I'm going to use this in the coming couple of weeks with my Year 9 and 10 classes. I hope it explains finding averages from frequency tables quite well.
Averages from Frequency Tables
ALL: Understand a method for finding the mode and median from a frequency table [L5] [E]
MOST: Find the median from a frequency table without converting the table to a list [L5] [D]
SOME: Work out a quick way to find the mean from a frequency table [L6] [D]