I've done a search for the answer but still couldn't figure it out.
Say for example:
Year 1 Result = 80% (Weight:20%)
Year 2 Result = 70% (Weight:10%)
Year 3 Result = Unknown (Weight:70%)
I've not yet got my results for year 3. I want to calculate what my average percentage is so far, based on year 1 and 2 and what I would need to achieve in my 3rd year with a weighting of 70%.