Let
be the amount Alice has just before the final swap, and let
be the amount that Betty has just before the final swap, Then, since Carol is going to give
to Alice and
to Betty, and retain 8 dollars for herself, she must, just before the final swap, have
.
So after the final swap, when each will have 8 dollars, Alice has
and Betty has
. Therefore
and
Now we can make a table of values going backwards:
Alice Betty Carol
After 3rd Swap: 8 8 8
Before 3rd Swap: 4 4 16
(Because Carol must have 8 left after she gives 4 to each of A and B)
Before 2nd Swap 2 14 8
(Because Betty must have 2 to give to A and 8 to give to C)
Before 1st Swap 13 7 4
(Because Alice must have 7 to give to B and 4 to give to C)
John

Egw to Beta kai to Sigma
My calculator said it, I believe it, that settles it