## The mathematical boundary between a joke and a lie

Like all siblings, my children occasionally quarrel. I generally try not to get involved unless it gets loud or one of them complains to me. Sometimes, however, I hear something that amuses me and I tune in or even join the conversation.

Today, it began with Zoe (5 yo) accusing Katie (9 yo) of lying to her. Katie, in her turn, was claiming that it was just a joke. This is how the conversation continued:

Katie: You don’t even know the difference between a joke and a lie.
Zoe: Yes I do.
K: Oh yeah, what is it?
Z: For example, if you say “I ate 100 crepes”, then that’s obviously a joke. But if you say “I ate all the remaining crepes”, then that’s either the truth or a lie.
K: That depends on how many crepes were left.

This is where I joined the conversation. I was very intrigued to find out exactly at which point the joke turns into a lie. So I started asking some questions of my own.

The girls agreed that at 50 crepes it was still a joke and at 5 crepes it was a lie (assuming you didn’t actually eat them). When I asked about 20 crepes, there was a brief pause, and then Katie said, “You have to know the person.”

So the mathematical boundary between a joke and a lie, like so many other things, depends on the person.