One's loss, another's gain
Jim walked into a grocery store and bought things worth $20. He gave a $100 bill to the shopkeeper Kane. Unfortunately Kane didn't had the change and exchanged the note with his partner Alex for ten $10 bills. Finally, Kane returned back the balance to Jim.
The next day Alex came to Kane and told him that the note he(Kane) gave to him was a counterfeit. Kane had to thus exchange it again for $100.
How much loss did Kane had to suffer at last?