The riddle
A Man Steals $100 From a Store. How Much Did the Store Lose?
The plain version
A man takes $100 from the store. Before, the store held $100 more than after, and nothing else has changed. The store lost $100. That is the puzzle in its simplest form.
The version with a purchase
Many tellings add a step. The man pays for something priced at $70 with the $100 bill he took and receives $30 in change. Track the store's cash: $100 taken, $100 paid back, $30 handed over, a net loss of $30 in cash. Add the $70 item that left the shelf, and the store is out $100 in all. Paying with its own money changed nothing. A version with a counterfeit bill reaches the same total: the store receives no real money, hands over $30 in change and gives up the $70 item, a loss of $100.
Where the other totals come from
Multiple-choice versions list answers such as $130, $170 and $200. Each can be reached by counting a piece twice. Adding the $30 change to the $100 gives 130. Adding the $70 item to the $100 gives 170. Adding both gives 200. The options $30 and $70 come from the opposite mistake, treating only the change or only the item as the loss. Writing each step on its own line, with dollars going out and in, shows which piece was counted twice.
Why people argue about it
Some online arguments about this puzzle come from measuring the $70 item at what it cost the store instead of what the store charges for it. The puzzle uses the price on the tag, so $70 is $70. A similar puzzle that hides a trick inside a count is the one about subtracting 5 from 25.