(Sorry for posting this in two forums, but I didn't know which one it fit under better.)

I am making a spreadsheet that requires multiple dates and percentages. Is there any way that I can make the percentage that is related to the most recent date weighted more than a percentage with a date from a month or two ago?

For example:
X//Y//DATE
90%//85%//3-March
85%//70%//21-May
87%//90%//6-June

Is there formula so that I can have the 90% and the 87% be the most important (or weighted), the 70% and the 85% be the second most important, and the 85% and the 90% be the least important when I average them out?

I'm working with about 200 cells to average (50 sets of 4) and I was wondering if there was a way that I could put a date in the same row as the data and, if I'm going to be changing the data and date regularly, have the spreadsheet automatically update the weight based off of the date's distance from today's date.

It's a little difficult to describe.

Think about it if I were doing it with polls.
If I have 3 polls with different dates of when they were surveyed, obviously the most recent poll is the most reliable, but it doesn't completely discredit a poll taken a week or two ago. So, is there a way that I can make the most recent poll weighted more than the other two when I end up averaging them out?

Thanks!