function to calculate the average price

It would be nice to have a function to calculate the average price of each runner based on its matched volume:

For example: odds  4.0    matched volume 2000
                      odds  5.0   matched volume   500

average price: 4.2

http://community.marketfeederpro.com/triggered-betting-10/how-to-get-average-price-based-on-matched-volume-1260/msg6368/?topicseen#msg6368

Thanks