Riddle posed to Inspector Colombo (who solved it), if you feel like it without cheating:
"In a room, there are several bags of gold ingots (as many as you want) and in each bag, there are several ingots (again, as many as you want).
However, in one bag, the ingots are fake gold and weigh one ounce less than the authentic ones.
The solver has a token scale and has only one token available (so only one weighing). How can they find the bag that contains the fake gold?"