Question of the day! someone steals your n500. same person owes you n100. so he uses the stolen n500 to pay you your n100, and you give him n400 how much did you lose? ?

Someone steals 500, your balance is -500
Same person gives you 100, your balance is -400
You give them the 400 change, your balance is -800

N500 because in total you owe the person N600 (N500 stolen, N100 owe) and you give the person you stole money from N500 and the person gives you N400 change + the N100 you still have remainder giving you N500 in total