The absolute correct answer to this puzzle is $400.
If you got confused, don't worry! Here are the two easiest ways to break down the math so it makes perfect sense:
Method 1: Treat it as two completely separate transactions
Transaction 1: You buy an asset for $800 and sell it for $1,000. Your profit is: $200 ($1,000 - $800).
Transaction 2: You buy an asset for $1,100 and sell it for $1,300. Your profit is: $200 ($1,300 - $1,100).
Total profit earned: $200 + $200 = $400.
Method 2: Total Outflow vs. Total Inflow
Total Money Spent (Outflow): $800 + $1,100 = $1,900
Total Money Received (Inflow): $1,000 + $1,300 = $2,300
Net Earnings: $2,300 - $1,900 = $400.
No matter how you look at it, you walk away with an extra $400 in your pocket!