Averages using Quarters & Months

Hi,

I've come across this issue for the past couple of years and never got around to solving it. I usually create a long work around but i think its time to ask the pros for a better method.

I'm trying to get a clean formula or clean vba code to do the following: Average the values of certain months that match the given quarter # and year. For example:

1) I have a cell with Q1-10 written it (general), and
2) cells with Jan-10, Feb-10, Mar-10 (dates) and next to these cells their respective values

Jan-10 100
Feb-10 25
Mar-10 25

i would like to get the average of Q1-10

My most recent method for solving this is as follows

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This formula entered near Q1-10 would find the specific months in Q1 and sum their values then divide by the number of months with available data

It works fine on my pc with excel 2007, but for some strange reason it doesnt work in other peoples excel 2007. Im sure there is a much simpler way to solve for this. Could someone pls advise

I would like to use a manual function in order to avoid manual mistakes.Im thinking something along the lines of Q1Average(Year, Range, Average Range)

where the funtion would immediatly look for Jan-10, Feb-10, Mar-10 in the relevant cells and just average out the numbers in the average range

Thanks for the help!