Have another row by the bills. If someone should not pay that bill put a "1" in it. Multiply the amount owed by (1-value). If they owe it, then they owe the amount. If the box has a "1" in it then it will be multiplied by "0" and be "0" owed by him.
Then you will need to figure that everyone else must pay more for this bill. With one "don't pay" row for each person, divide the total by (4-1val-2val-3val-4val) If all four people should not pay that bill then you have problems, but otherwise it will be OK.
Expand on this idea and add it to all the bill and recept rows and you will be good to go until the next revision is needed.
Re: OT: Spreadsheet Fun!
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