Well done. Both sides of the negotiation have equal added value. Think about the last negotiation Adam has with a red card holder. To get that last $100, Adam needs the last red card just as much as the red card holder needs Adam’s black card. The two sides are perfectly symmetric. Thus we expect that negotiation to result in a 50:50 split. But since everyone can hold out to be last, the same split should follow for all holders of a red card.