Let’s share some riddles.

You can post riddles in every language.

Please hide solutions and tips as spoilers.

I actually have one riddle I’m trying to solve for months now.

Here it is in German:

Du und ein anderer Astronaut seid die einzigen 2 Überlebenden eines schrecklichen Weltraumunfalls im Orbit um einen fremden Planeten. Du hast noch gesehen wie dein Partner, so wie du auch, in einem sicheren escape-pod Richtung Planetenoberfläche trudelt, dann verlierst du ihn aus den Augen. Ihr stürzt beide an unterschiedlichen, zufälligen Orten auf dem Planeten ab. Ihr wisst voneinander, dass ihr den Absturz dank der escape-pods sicher überlebt habt, habt aber keine Ahnung wo ihr abgestürzt seid.

Die einzige Möglichkeit den Planeten wieder zu verlassen ist euer Teleporter. Du trägst nur einen Teil davon bei dir und du weißt, dass dein Partner den anderen Teil hat. Alleine sind die beiden Teile nutzlos, ihr müsst zueinander finden um die beiden Teile zusammenzufügen und euch zurück auf das Mutterschiff zu beamen.

Was machst du, um möglichst schnell den anderen Astronauten zu finden und euch beide zu retten?

Regeln:

- Alles ging so schnell, du konntest dich vorher nicht mit deinem Kollegen absprechen (kannst aber davon ausgehen, dass er ein ebenso begnadeter Denker ist, wie du selbst)
- Du hast natürlich keine Technologie, Instrumente oder Messgeräte, das wurde alles beim Aufprall zerstört
- Du kannst dich überall auf dem Planeten frei bewegen (also keine Ozeane oder Klippen die den Weg versperren) und Essen und Trinken bietet der Planet genug.
- Du kannst keine Nachrichten hinterlassen oder Wege markieren, der Wind verweht jegliche Spur sofort
- Die Sonne dieses Planeten geht ähnlich der Erden-Sonne regelmäßig auf und unter, verursacht also Tag und Nacht und bietet dir einen Anhaltspunkt zur Orientierung.

One of my favorites:

100 prisoners get a chance to solve a riddle and be free, but if they don’t solve it they get a life sentence.

There is a room with 100 boxes.

Each one has a number from 1 - 100 on it (each number once).

In each box there is a ball with a number from 1 - 100 on it (each number once).

The balls are distributed randomly.

The prisoners also all have a number from 1 - 100 (each number once).Now each prisoner one by one has to enter the room and open up to 50 boxes. Each prisoner has to find their own number. If even one prisoner fails they all stay in jail for life.

They can’t take the balls out of the boxes or leave boxes open - no communication or leaving signs - but they are all very smart, so they’ll find the same solution.

How can they win with a 50%+ chance?

## Solution, I guess

They both walk to the middle of the planet.

## Re: Lidwiens Solution

What do you mean with middle? The equator? Or are you a flat-earther?

## not the solution, I guess

I meant the equator. But on second thought that wouldn’t work.

## Spoiler

You go to the north constantly, orienting yourself with the sun, until you reach the pole, and hope your friend will do the same. You join him there.

## Re: Spoiler

There is no logical way to know which pole to choose, so I don’t think that’s it.

## Spoiler

The first fellow opens 50 random boxes, and has a 50% chance of opening his number. Then he sorts all the boxes on number (putting the box vertically if he opened it). This communicates to the next person exactly which box to open. Hence it all relies on the first person having the luck of the draw of 50%.

**Edit by @alex21**: I put your answer in a details tag to keep the fun

Everybody leaves the room as is.

## Spoiler

Then, depending on their season in their respective hemisphere, they go to the pole where it is always the day (but it doesn’t work if it’s autumn or springs…).

## Spoiler

And if the guardians mix the boxes between each prisoner?

## Some reflexion...

The thing is, whatever you do, there is nearly always a chance that your partner will do the exact opposite (apart if you dig to the center of the planet, but it’s not really an option). I was suggesting north pole because this seems sensible to me, and so both might do it.

I think all is in the “nearly”.

Otherwise a friend of mine suggested starting forest fires, so that the other can either know where you are from far away (but not on the scale of a planet) or know whether you already passed at a given place (but then as said in the riddle you can’t leave any signs).

## Summary

Yes well it is possible to add all kind of rules to a riddle apart from the written text. Especially if it supports the projected outcome.

Another solution is to bribe the guards.

## Summary

## Idea for a solution regarding the astronauts

I guess it would work, if both start from the landing point moving clockwise in a spiral / widening circles around the landing point.

This way they should sight each other at one point.

Drawback is that they will have to walk a very long way. Depending on the size of the planet they might die of old age before meeting each other.

## Idea for a solution regarding the boxes

I guess, they start by opening the box with their own number. If there is a ball with a different number in it, they open the box with the number on the ball. If there is the wrong number in that box, they open the box with the number of that ball and so on.

I can not really explain right now, why that should work. But at least they do all follow the same system.

Eine Frage, gibt es eine definierte Lösung?

## Another idea for astronaut problem

As other people mentioned, the poles seem to be the only places that seem to be unambiguous according to the setup. I propose a solution that I think works. Without a compass, I suppose that the way you determine north is to set up a stick on some platform, and measure the length of the shadow as the day passes. The time at which the shadow is shortest (assuming the ground is level), the shadow will be pointing due north or south - unless you’re very unlucky and the sun is directly overhead. Measure the length of the shadow so you can guesstimate your altitude, in case the axis tilt is known. In the case that you’re unlucky and the sun is overhead, you’re close to the equator and can orient yourself reasonably easily with respect to sunset/sunrise. In any case, once you know where the north/south line is, you can determine which direction north is from the place where the sun rose.

Repeat the experiment when you walk in that direction. Assuming that the sun is in the sky often enough, it may then help to further orient oneself with respect to the sun, heading out a bit after solar noon so you can make your measurement. If it’s night, you’ll have to make a star chart, finding out which star does not change position - or simply wait until the sun rises again (may be some months!) With this approach, you’ll have made it to the pole of your choice. Edit: if we know that the other person will also choose the north pole, we are done here.

Edit: The following was my proposal to get rid of disambiguity if we cannot know that the other person chose the north pole. It does not seem to work in all cases.

Then, my proposal is to wait at the pole for twice as long (you can at the very least measure days having a sundial and counting the number of times it goes around your sundial. Make sure not to move your bed! This will mark the orientation.) as it took you to get there. If you’ve waited and your friend is not there yet, head to the other pole. Again, once you get there, wait for twice as long as it took you to get there - excluding in your time count days that you are at the pole and it is night.

Edit: I’ve started thinking that my “wait for twice as long” condition is not sufficient. What if they are both equal distances from the poles, but they choose the opposite poles? They’ll be stuck chasing each other. I suppose the method is unambiguous (there is only one north pole by the definition) if we know that the other person will also choose the north pole from the start. In this case, we don’t need to change the pole we go to. I’m not sure if there’s a way to break the symmetry if we know the other person will make sensible choices, just not which one…

Alternate method for finding north/south: split the angle between shadows cast at sunset and sunrise, although this depends on having a flat horizon.

I’m also a fan of this solution! Just meet at the core!

I just now looked it up.

- So far, I didn’t find the riddle of the astronauts. No solution as well of course.
- For the 100 prisoners, there is a solution easy to find on the web. Wikipedia: 100 prisoners problem (it’s rather complex math)