Does any one know how to do a weighted average (sumproduct/total) in matrix in SSRS 2008

I have just started using SSRS 2008开发者_如何学Go and needs to have a weighted avg for the columns. I know there a recursive sum, but not sure how to use it and achieve it?

If M is month, V is value then I need weighted avg = M1V1 + M2V2 + M3V3 / V1+V2+V3.

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The expression

=Sum(Fields!M.Value*Fields!V.Value)/Sum(Fields!V.Value)

should do the trick