It was a simple one really, something that's making the headlines everywhere and hard to get away from.
"Who are the G20?" Or put another way, "Which countries have sent their head of state or government to the meeting in London?"
Go ahead. If you have time, grab a pen and a piece of paper and try answering that without cheating or Googling.
That's what I did, and this is how far I got.
"Well to begin with," I told him there are the members of the G8. That's easy. It includes the UK, the US, France, Germany, Italy, Canada, Japan and Russia."
Then I thought for a while.
"China and India naturally. They should have been part of the club a long time ago," I wisely informed him.
"In fact at the last G8 meeting in Hokkaido, Japan, that's exactly what the French president, Nicolas Sarkozy wanted. But nobody listened to him then."
Yes the poor boy was getting a mini politics lesson as I was just warming up.
"Brazil," I said confidently. "And Saudi Arabia."
I was beginning to crack though, I could feel it.
"Um South Africa and A r g e n t i n a," I rather dragged the last name out as horror of horrors, I was quickly running out of steam.
Now this is the point at which I could have changed the conversation or simply huffed and puffed my way through an answer.
But that wouldn't have been fair to him, and besides it's not really my style.
"You know what?" I said. "I don't know the names of the other countries. I should. But I don't. Shame on me."
So we did what we should have done right at the beginning and Googled, coming up with the five missing pieces of the puzzle. Mexico, Turkey, South Korea, Indonesia and Australia.
And of course we discovered (as you either already knew of have since found out yourselves) that there aren't actually 20 countries that are "members" of the G20, but 19.
Oh yes and we also saw that there are "non-members" present in London from the Netherlands, Spain and Thailand, which of course raised two more questions from that teenager.
"What's a non-member?" and "Do they get to eat at the dinners?"
Thank goodness he didn't ask me to name all the leaders.