I'm still puzzling over this one. After 40 years, are you absolutely positive you have written the riddle in EXACTLY the same way it was written for you? Alost all riddles hinge on the exact wording, because sometimes they are relying on a word having multiple meanings, so the question is not the question you think it is at first. And sometimes they are relying on misdirection, so a part of the question is irrelevant. If the riddle is not asked the right way, it cannot be answered. Often, if you've heard a riddle and not figured it out, you might ask someone else to solve it, but you rephrase it based on your own mis-interpretation of the misdirection.
For example, if the questions were:
There are three ways to spell the word "to". What is the proper way to the end that sentence?
Then one possible answer would be "with a period." (Or with a quotation mark, depending on your style rules!) I'm not saying that is how your riddle is supposed to be phrased or that this is the right answer. I'm just saying the exact wording matters.