Beat The Banker / Deal or No Deal Odds Calculation Help...

Hello.

I'm trying to work out how the banker on the UK T.V. show "Deal or No Deal" Works out the Math of what Prize to offer a contestant

If you haven't seen the show General description follows

Contestant Chooses A Random Unknown Prize Between 1p to £100..


Prizes Increment As

1
5
10
50
100
200
500
750
1000
1500
2000
2500
3000
3500
4000
5000
6000
7000
7500
10000


(These are My Variables I wish to program), Depending on what Prize Boxes are left after the contestant has randomly chosen 1 of 20 Prize Box
Contestant Has Taken One of These Values Away Then Takes 5 of the values out of the " Pool " after those 5 are taken away a Sum is offered for the contestant to walk away with that sum or Gamble and take away Another 5 boxes Then a new offer is made for the Contestant to walk away.. etc etc until all boxes are opened or until Contestant Walks.

If at the end of this the Contestant Remains and The only Prize boxes Left Have the values 1 and 10000 The Offer would be 5000 That is as my mathematics skills Will allow me to Imagine..

I Need the formula to work out the value to Offer as the Contestant Plays the game

Hope that Makes Sense Cheers..