A very simple but confusing puzzle.
a lady buys goods worth rs. 200 from a shopkeeper who sold her the goods at zero profit.
the lady gives him a 1000 rupee note. the shopkeeper gets the change from the next shop and keeps rs. 200 for himself and returns rs. 800 to the lady.
later, the shopkeeper who gave him the change comes with the 1000 rupee note saying it is 'duplicate' and takes his money back.
how much loss did the shopkeeper suffer?