I am not trying to estimate the payout...i am trying to adjust the final payout as if i had placed my bet.....it is a part of my test to see if the ratings i have are profitable to bet the quaddie with....at the moment with a small sample of 30 races i have 9 winning quaddies with an average divi of $3,500

OK that is a different matter.
If you only want to check on the results, then see my first reply.
You only take out 20% from "your" bet not the pool, because, since the divi is declared, obviously the 20% had been taken out of the pool.
Good luck with it!