The Riddler

My husband loves riddles.  For Valentine's Day, he couldn't just give me my card, he had to give me a riddle instead.  The answer to the riddle would lead to the card.  I remember the first birthday I celebrated after we were married: he left clues, from one to the next, all around the house that I had to follow in order to finally discover my gift.  Sometimes these riddles are fun; sometimes they are extremely frustrating.

My husband's family was visiting this past weekend and much of their time was spent puzzling over his riddles.  His younger brothers love to stretch their minds, and my husband was happy to give them the opportunity to do just that.  Hour after hour was spent challenging, stretching, and frustrating their minds.

The last night they were here, the two brothers were still trying to figure out one last puzzle.  They had been trying for nearly half the day.  They decided to give it one last attempt before going to bed and heading back home in the morning.  Try as they might, they still couldn't get it.  The youngest brother pleaded with me to tell him the answer.  One of the rules of the game, though, is that no one who knows the answer is allowed to share that information.  I, in my empathy towards my brother-in-law, felt no reason why I couldn't give him clues--albeit, clues that closely resembled the actual answer.  My husband was furious; my actions were against the rules.  I was not so bothered.  Why couldn't his brother know?  He would be plagued for the night, if not subsequent days, without the answer.  What could it hurt to tell him?  At least he could get a good night sleep.

Perhaps it's best that my brother-in-law couldn't seem to grasp my well-informing hints.  He never got the answer.  This was an easy resolution to the debate over whether it was appropriate to give away the solution.  I had never realized how much more of a law-abider my husband is than I.  Now I am revealed for the rule-breaker that I am.  And I am not ashamed.

So, on that note, here are some of the riddles that my husband used to disarm his brothers on their visit.  And, like I said, I am not held by any law of riddle-ology.  If you want the answers, feel free to ask.  I willingly give that information to any who request it.

Riddle 1:
Petals Around the Rose

Riddle 2:
(taken from this site: physics forum)
30 Prisoners are on death-row. The prison warder doesn't view their crimes with much seriousness,and decides to give them a chance to escape.  He offers the following:
Tomorrow all of you (the prisoners) will be blindfolded, and either a black or a white hat will be placed on your heads. You will then be placed in a row, all facing the same direction, all in a straight line (so all but one is facing someone elses back). Then your blindfolds will be removed. You cannot see your own hat, or those on the people behind you. But you can see all the hats of the people in front of you.
The offer is escape from execution, if you can guess what color hat you are wearing. You have the opportunity to say one word: "black" or "white."  Nothing else.  If you guess correctly, they you be freed. Otherwise, death.
What strategy can be used to maximize the number of prisoners freed, assuming they get a chance to discuss a plan that same night (ie:prior to being lined up)?  What is this strategy, and how many prisoners will be guaranteed their freedom? 


Riddle 3:
(taken from a fantastic comic for silly smart people: xkcd)
A group of people with assorted eye colors live on an island. They are all perfect logicians -- if a conclusion can be logically deduced, they will do it instantly. No one knows the color of their eyes. Every night at midnight, a ferry stops at the island. Any islanders who have figured out the color of their own eyes then leave the island, and the rest stay. Everyone can see everyone else at all times and keeps a count of the number of people they see with each eye color (excluding themselves), but they cannot otherwise communicate. Everyone on the island knows all the rules in this paragraph.

On this island there are 100 blue-eyed people, 100 brown-eyed people, and the Guru (she happens to have green eyes). So any given blue-eyed person can see 100 people with brown eyes and 99 people with blue eyes (and one with green), but that does not tell him his own eye color; as far as he knows the totals could be 101 brown and 99 blue. Or 100 brown, 99 blue, and he could have red eyes.

The Guru is allowed to speak once (let's say at noon), on one day in all their endless years on the island. Standing before the islanders, she says the following:

"I can see someone who has blue eyes."

Who leaves the island, and on what night?


[There are no mirrors or reflecting surfaces, nothing dumb. It is not a trick question, and the answer is logical. It doesn't depend on tricky wording or anyone lying or guessing, and it doesn't involve people doing something silly like creating a sign language or doing genetics. The Guru is not making eye contact with anyone in particular; she's simply saying "I count at least one blue-eyed person on this island who isn't me."

And lastly, the answer is not "no one leaves."]