Both you and your brother calculations are correct. You remove the expenses and split the profit:
Revenue - Expenses = Profit share = Profit/2 1000 - 200 = 800 800 / 2 = 400 Both should get 400 of **profit**.
He splits the revenue and the expenses:
(Revenu/2) - (expenses/2) = share (1000/2) - (200/2) = 500 - 100 = 400 Both should get 400 of **profit**.
As far as the computation goes, the result is the same. They both get \500 of the revenue except for the fact that the revenue money doesn't exist if your brother collected the money and paid the expenses. Once you have paid the expenses, what is left is profit, not revenue.
The problem here is that we don't know who got the 1000. We know your brother paid \$200, but we don't know who collected the \$1000.
If your bother collected the money and paid the expenses, what is left is profit: he owes \$400 to his partner. If he likes, he can give \$500 to his partner and take \100 back. No difference.
If his partner collected the money but did not pay the expenses, what he has is revenue, he owes your brother \600. His partner can also give him \$500 for his share of the revenue, and \$100 for his share of the expenses.
Worth mentioning that whoever owns the car is the sucker in this deal, because the real cost of the car is quite a bit in excess of the gas in the tank. There are insurance fees, maintenance, repairs, depreciation, risk, etc. which all add up to the actual cost of driving the car. Roughly, if you spend \$200 on gas, there is about \$100 in hidden costs.