Here’s a fantastic problem I recently heard. Apparently it was first posed by Claude Gaspard Bachet de Méziriac in a book of arithmetic problems published in 1612, and can also be found in Heinrich Dorrie’s 100 Great Problems of Elementary Mathematics.
A merchant had a forty pound measuring weight that broke into four pieces as the result of a fall. When the pieces were subsequently weighed, it was found that the weight of each piece was a whole number of pounds and that the four pieces could be used to weigh every integral weight between 1 and 40 pounds. What were the weights of the pieces?
Note that since this was a 17th-century merchant, he of course used a balance scale to weigh things. So, for example, he could use a 1-pound weight and a 4-pound weight to weigh a 3-pound object, by placing the 3-pound object and 1-pound weight on one side of the scale, and the 4-pound weight on the other side.
The solution to this puzzle is really fascinating and leads into all sorts of fun generalizations and other topics; I’ll write more later. For now, as always, feel free to leave questions, observations, and solutions in the comments (so don’t look at the comments before you’ve solved it if you don’t want to see the answer!).