Answer by
jsmith (2067)

The function you want to use is SUMPRODUCT(). For example, the following formula in a cell -
SUMPRODUCT(B4:B6, A4:A6) / SUM(A4:A6)
would give the weighted averages in the cells B4-B6 weighted by the values in A4-A6. Expanded, the SUMPRODUCT function looks like (B4 x A4) + (B5 x A5) + (B6 x A6)