At the end of the 1970s, researchers at the Institute for Research on Mathematics Teaching (IREM) in Grenoble, France, gave primary-school children a strange problem: There are 26 sheep and 10 goats on a ship. How old is the captain? The problem has no answer: nothing in it mentions anyone’s age. Even so, according to the account that the educator Stella Baruk made famous in her book L’âge du capitaine (1985), 76 out of 97 children answered with a number, almost always $36$, the sum of the two that appeared in the text.