===== Answer ===== 

$2

The total amount of money they get from selling the camels will be //N<sup>2</sup>// where //N// is the total number of camels. The number of sheep they can buy will be //N<sup>2</sup>/10//. If they cannot split the sheep evenly, the number of sheep must be odd. If you look at the sequence of possible number of sheep for //N = 1-100//, all odd values will leave them with $6 left over to buy the goat. This leave Jack with $4 worth of animal more than Bill. By giving up his dog and giving it to Bill, he takes $2 away from himself and gives it to Bill.