Weighted averages - no easy way???

[trstew]

I need to come up with a single figure (# of days) for costs occurring on various dates (expressed as # of days since 11-21-16) that will express that figure weighted as to the amount and how long ago (# of days) it occurred. I think SUMPRODUCT can be utilized, but am not sure how...

[TheN]

you have sumproduct applied correctly in there.

I just did it manually so you can see what I mean.

See attached file.