Even better: ask it something you just made up.
For GPT, there's no real difference and you shouldn't expect any.
The correct conclusion is not that 50% of kids are dumb and 50% smart. Actually, none of the kids knew but they had a 50% chance of picking the right answer at random.
Knowing what you don't know is an "advanced" skill many adults haven't even mastered. I'm not at all surprised chatGPT struggles to not-answer questions on things you just made up.
I can remember being a child and having this belief, but it wasn’t based on a guess. To me, it was logical.
I thought that because fish and chips accompanied each other on the plate, they probably also accompanied each other in the sea. I can distinctly remember picturing fries swimming around with fish, in what I imagined to be their natural habitat.
I think it gives you more insight into what GPT actually is than just seeing it being wrong about something you're knowledgeable in (which shouldn't really be surprising).