Maybe this?
A
B
C
D
1
 Year teams Finished %
2
2013
10
10
0%
3
2012
9
7
22%
4
2011
8
4
50%
5
27
21
22%



Jeff asked
Can you give a couple of examples where you also tell us the resulting percentage that you expect?
I dont see any samples in your reply to him?
D2=(B2-C2)/B2 copied down
B5=SUM(B2:B4) copied to C5

It is not a good idea to take an average of percentages, that is the same as taking an everage of averages...mathematically incorrect. I summed the 2 columns and used the same formula from above