A lady buys goods worth rupees two hundred from a shop, ( shopkeeper selling the goods with zero rs. profit).
the lady gives thousand-rs. note.The shopkeeper gets the change from next shop and keeps rs.two hundred- with him and returns rs, hundred to the lady.
later the shopkeeper of the next shop returns the thousand-rs note saying its duplicate
and takes his money back
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he returned the asli two hundred+800 his own to the shopkeeper
so lost 800 plus 200 worth of goods.
the lady got 800 genuine+200worth of goods. (total 1k for paying nothing)
shopkeeper of next shop lost nothing.