Answer: Tuesday Teaser #3
This is a classic in that it’s easy to solve if you think about it in the right way, but very difficult if you start thinking about it the wrong way. When I first heard this puzzle I started thinking that there might be a situation where one ant keeps bumping into other ants and ends up staying on the stick for a long period of time. My girlfriend, on the other hand, got the answer straight away.
The key to this was one simple observation: Instead of thinking about the ants bouncing off each other, imagine them passing through each other and carrying on. This scenario leads in exactly the same outcome (as long as you don’t care which ant is which), but now it’s dreadfully easy to find the time by which all ants will fall off the stick - it’s the time it takes one ant to go from end to end, i.e. one minute.
