1. Monty Hall Problem
Still don't believe it?
Let's say you picked door number 1. Here are all the possibilities of what could happen:
Wait, you still have doubts?!
...this all assumes you wanted the car and not the goat.
2. 0.999... = 1
3. There are as many even numbers as natural numbers
4. Benford's Law
5. The Birthday Paradox
6. The Broken Water Heater Problem
7. Bertrand's Box Paradox
8. How To Estimate π From A Dart Board
9. The Harmonic Series Diverges To Infinity
10. Your Friends Are Probably More Popular Than You
11. A Perfect Parallelogram From A Wacky Shape Every Time
12. The Three Prisoners
The problem first appeared in legendary Martin Gardner's "Mathematical Games" column in Scientific American.
Source: Walter Hickey / Business Insider