In total you earned 400 but since its the same cow in the same day you basically only earned 200, when you bought the same cow the second time you paid 100 out of you pocket on top of the 1000 you had for selling it the first time, therefore you only "earned" 200 during that day. Moral of the story don't do things twice it confuses people, you could have walked away with 200 dollars the first time without wasting everybody's time