Initially, the cow is bought for $800 and sold for $1000, resulting in a $200 profit.
Then, the cow is repurchased for $1100. Considering the previous profit, the effective cost for this purchase is $900.
The cow is sold again for $1300, yielding a profit of $400 ($1300 – $900).
In summary, the correct answer to the puzzle is $400, achieved through understanding the profit made at each transaction.