@ Russian Roulette puzzle:
Still haven't really found the logic behind it. It's all about probability, and recognizing the limitations of the puzzle. If you were to fire shot one and it was blank, that means out of the next 5 chambers, 2 of them are deadly. Thus, 2/5 or 40% chance that the next shot is deadly if fired without a respin.
However, if you were to spin again, you'll reset the whole problem and have a 2/6 chance, or a 33% chance at having the next shot being deadly.
This math COMPLETELY works with the problem, but misses one vital important fact detailed in the problem that changes one of the probabilities. Think about what key piece of information is missing, and think about how that one piece of information can change the answer above.