#### How much loss is incurred due to a counterfeit note?

Alice visits a gift shop to buy a gift. The gift costs $7. Alice gives the shopkeeper (John) a $10 bill.

Since John does not have change, he asks his friend Tom for change. Tom gives him the required change; and John gives alice the gift and $3 in change.

Ten minutes after Alice leaves the shop, Tom comes to meet John and informs him that the $10 bill is a counterfeit.

How much loss did John make?

When we did this at a training session, there were all kinds of answers ranging from $0, $10, $13, $17 to $20. What do you think is the answer? And, why?