Originally Posted by rhizome

That's the right answer. It's pretty simple. They agree to pool their money together (and I assume split the profit fairly). Initially they both put $200 on the table but later on both accepted player B's extra $200 contribution. This means total pool is $600 with $400 of it contributed by player B. It is player A's responsibility to now hand over $333 of the $500 pool to player B leaving him with $167 and a net loss of $33. And player B will have $333 and a net loss of $67. The whole thing was handled poorly - once player B wanted to buy-in again, player A should have either said I don't want a part of it or contributed $100.