Post all your riddles in here, i love them.
Here is one i [surprisingly] didn't get. It's pretty easy though so only the dim ones won't get it.
Picture a square. Each with 4 sides, as they do. All the sides are the same length. A man walks around the square and it takes him 1 hour and 20 minutes to walk down each side except for one which took him 80 minutes. Why did it take him 1 hour and 20 mins to walk the other 3 but only 80 minutes for the other one?
He walks at the same speed, he doesn't magically develop wings nor does he get on a bus etc, etc.
(this one isn't as good to explain in writing, better when you draw it)