if(r < 4, 120 - (r * 20), n - r + 6)
Unless, as Magic_fubu noted, you were intending it to be 100 for 1st, 80 for 2nd, 60 for 3rd, 40 for 4th, 20 for 5th, etc. Which, again as Magic_fubu noted, is as far as you can go with that. The above yields the following for 20 players:
1: 100.00
2: 80.00
3: 60.00
4: 22.00
5: 21.00
6: 20.00
7: 19.00
8: 18.00
9: 17.00
10: 16.00
11: 15.00
12: 14.00
13: 13.00
14: 12.00
15: 11.00
16: 10.00
17: 9.00
18: 8.00
19: 7.00
20: 6.00