Some riddles are difficult because the math is complicated. Others are tricky because they make us **look at the same money from different angles**. This classic shopkeeper riddle is a good example: the numbers are simple, but following the money can make the answer surprisingly confusing.
> A man walks into a shop and steals a $100 bill. He then uses that same $100 bill to purchase $70 worth of merchandise. The shopkeeper accepts the bill and gives him $30 in change.
>
> **How much does the shopkeeper actually lose?**
The answer is **$100**, not $200 or $130. First, the thief steals $100, leaving the shopkeeper $100 short. He then returns to the same shop and uses that stolen bill to buy $70 worth of goods. The shopkeeper accepts the bill and gives him $30 in change. Although the $100 bill returns to the register, the shopkeeper has now handed over something worth $100.
The thief leaves with **$70 worth of merchandise and $30 in cash**. Together, that equals:
**$70 + $30 = $100**
The important point is that the original $100 bill should not be counted twice. It was stolen, but then returned to the shop as payment. What matters is what the shopkeeper is missing after the entire transaction is complete: **$70 in merchandise and $30 in cash**.
This is why adding $100 stolen + $70 merchandise + $30 change to get $200 is incorrect. The $70 and $30 already represent the $100 value the thief takes away. Likewise, saying the loss is $130 counts part of the transaction twice.
The easiest way to understand the riddle is to ignore the movement of the physical bill and compare the shopkeeper’s position before and after everything happens. In the end, the shopkeeper has lost **$100 altogether**.
The real trick isn’t difficult arithmetic. It’s learning to **track the value of an object through several transactions without counting it twice**. Sometimes the hardest part of a simple riddle is deciding which numbers actually belong in the calculation.
