Why is the difference in net cost 50 for every 25 bucks less I sell laptop 1 for and not 25? I mean if I make 25 less profit, the net cost should be 25 higher and not 50? Yes, I know I'm retarded :(

laptop 1 bought = 383,54
laptop 1 sold = 500
profit = 116,46
laptop 2 (net)cost: 649 - 500 - 116,46 = 32,54

laptop 1 bought = 383,54
laptop 1 sold = 475
profit = 91,46
laptop 2 (net)cost: 649 - 475 - 91,46 = 82,54

laptop 1 bought = 383,54
laptop 1 sold = 450
profit = 66,46
laptop 2 (net)cost: 649 - 450 - 66,46 = 132,54