There is a king. Not a crazy, murderous king like the other riddles, this one is actually kind and wealthy, and as such you would like to marry one of his three daughters. These daughters, while lovely creatures, can only answer yes or no questions. The eldest daughter always tells the truth, the middle daughter always lies. The third daughter is crazy and will answer any question randomly, either yes or no. You crave stability in life. You would like to marry the one who always tells the truth, but you are willing to settle for the one who lies all the time just because at least you will know where you stand. You do NOT want to marry the crazy one under any circumstances.
The big day comes when you make your choice. The king brings out the 3 ladies but you have no idea which one is which. You are allowed to ask ONE of the ladies ONE question, and then make your decision based on the answer. Note that your question must be answerable (ie you can’t ask unknowable questions like “Is there a God?” or logically unanswerable questions like “would the crazy person answer yes to this question?”). What question will you ask to guarantee marrying either the liar or the truth-teller?
No spoiling if you already know this one, please!