Brain Teasers
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Two trains are 100 miles apart, heading toward each other at 20 mph each. A fly starts on one train, flies to the other at 30 mph, then bounces back and forth until the trains collide. How far does the fly travel in total?
Research Clues
About expert brain teasers
Expert brain teasers aren't just hard — they're counterintuitive. The correct answer feels wrong even after you've seen the proof. Monty Hall is the poster child: switching doors gives you 2/3 odds, not 1/2, and it takes most people a simulation (or a lot of arguing) to accept it.
The key at this level is to distrust your gut completely. Set up the problem formally — probability trees, explicit counting, whatever framework forces you to be precise. Intuition fails on these by design. The math doesn't.