In fairness, this can catch people out and if you're not listening, it can get a little embarrassing.
It's pretty straightforward. Two brothers, one of them is four years old and the other is half his brother's age. How old will the younger brother be when his older brother is 100?
Don't say anything, just click the video and see.
Yes, there it is.
Half his age at four would be two, meaning he's two years younger than him - so at 100, he'd be 98. Now, go out there and make eejits of your friends and family and don't forget to film the whole thing for proof that anyone can be made look stupid.