Short Answer 
The total earnings from the cow transactions were calculated as follows: a profit of $200 from the first sale, a loss of $100 from repurchasing the cow, and a profit of $200 from the second sale, resulting in total earnings of $300.
Step 1: Calculate the Profit from the First Sale
To determine earnings, start by calculating the profit from the initial sale of the cow. When you sold the cow for $1000, you had initially bought it for $800. The profit here is calculated as:
- Profit = Selling Price – Cost Price
- Profit = $1000 – $800 = $200
Step 2: Assess the Loss from the Second Purchase
Next, analyze the loss incurred when you repurchased the cow. You bought it again for $1100 after selling it. The loss is computed by comparing the purchase price to the selling price from the previous transaction:
- Loss = New Purchase Price – Previous Selling Price
- Loss = $1100 – $1000 = $100
Step 3: Calculate the Profit from the Final Sale
Finally, calculate the profit made from selling the cow a second time for $1300. By comparing this to the last purchase price, you can find the new profit:
- Profit = Selling Price – Cost Price for Last Purchase
- Profit = $1300 – $1100 = $200
Adding these results together gives the total earnings: $200 (first sale) – $100 (loss) + $200 (second sale) = $300.