I remember one year in maths class. The first lesson of the school year was on probabilities, and the teacher explained how to calculate the probability of an event when you have n possible and equally likely events and m of those are desirable, as the fraction m/n.
She worked through a couple of examples with us and gave us a few more to do on our own.
After we had had some time to do them, she asked us to present our solutions and we'd discuss them.
One of those questions was along the lines of "If you put all the letters of the alphabet into a bag and draw one out, what is the probability of drawing a vowel?"
She "obviously" expected the answer to be 5/26, but the first student she asked said something different—I have an idea it was Elsa Moya from Spain and that she said 1/6 instead.
This confused the maths teacher at first until she asked her how she had calculated that, and she said that there were 30 letters in total, of which five were vowels, so the probability was 5/30 = 1/6. (This was around 1990, and I imagine she had added ch, ll, ñ, and rr to the 26 letters in the English alphabet; I believe that some of those are no longer considered separate letters in Spanish but are rather treated like English sh—a digraph, that is, two letters that together signify one sound.)
That's what comes from teaching at an International School :)