I will try to explain this as best I can. I have a series of numeric progressions (all integers, decimals are to be dropped) that I need to be able to calculate in Excel. Here they are:
L L*.75 L/2 (L-1)*.8 (L-4)/3 ?

1 0 0 0 0 0
2 1 1 0 0 0
3 2 1 1 0 0
4 3 2 2 0 0
5 3 2 3 0 1
6 4 3 4 0 1
7 5 3 4 1 2
8 6 4 5 1 3
9 6 4 6 1 3
10 7 5 7 2 4
11 8 5 8 2 4
12 9 6 8 2 5
13 9 6 9 3 6
14 10 7 10 3 6
15 11 7 11 3 7
16 12 8 12 4 8
17 12 8 12 4 8
18 13 9 13 4 9
19 14 9 14 5 9
20 15 10 15 5 10
The first column (L) is the level of the progression. The next four columns are progressions I have figured out. The formula for each one is in the header.

It's the last column that I can't figure out. How would I express that using a formula? I know I can do an Index (Array?), but that seems so clunky.

Your input is greatly appreciated.

...I sat there staring at it for at least 10 minutes
and couldn't figure it out. I don't remember enough
Trig or Calculus(sp?) to even begin to figure it out.

I'm obviously not as smart as you are. But this is now
a quest for me to find the formula!!

and how much of my final grade does this account for?

and how much of my final grade does this account for?two thirds ;)