A trader marked his goods at 20% above the cost price. He sold half

Hello VeritasKarishma, Bunuel could you please explain the solution to this problem ?

I used the method provided on one the posts which emphasizes the relation between marked up prices and profits -->

(1 + Markup %) (1 - Discount%) = (1 + Profit%)

Using this formula, I got the following --> Profit of 20% for half of the items, Loss of 4 % for a quarter and Loss of 28 % for the other quarter

After this to calculate total gain, I just assumed there are a total of 4 items each at a cost price of 10$. I split these 4 items into the following.

1) 2 items with a profit of $2 (20% of Cost Price for each item) -> Total Profit = $4
2) 1 item at a loss of $ 0.4 (4% of Cost Price for each item) -> Total Loss = $ 0.4
3) 1 item at a loss of $ 2.8 (28% of Cost Price for each item) -> Total Loss = $ 2.8

When I use the above numbers to calculate percentage, I get ([4 - (0.4 + 3.2)] / 10) * 100 = 0.08 = 8 %

What am i doing wrong here