A dragon and knight live on an island. This island has seven poisoned wells, numbered 1 to 7. If you drink from a well, you can only save yourself by drinking from a higher numbered well. Well 7 is located at the top of a high mountain, so only the dragon can reach it.

One day they decide that the island isn't big enough for the two of them, and they have a duel. Each of them brings a glass of water to the duel, they exchange glasses, and drink. After the duel, the knight lives and the dragon dies.

Why did the knight live? Why did the dragon die?

Welcome to Synth.  He's probably asleep already, as I should be.

Hmm, maybe the knight brings water from well 1? No matter what well the dragon chooses it will be a higher number, and when they exchange glasses, the knight automatically chooses a number that is higher than the dragons number (which is 1), and therfore the knight lives, and the dragon dies?

Uhh... if the knight gave the dragon water from well 1, then the dragon could save himself by drinking from any well...

Then again, on the face of it the dragon can save himself from whatever the knight brings him by going and drinking from well 7, so who knows.

Unless the knight slipped a little something extra into the dragon's water, above and beyond the normal well-poison 

so...the dragon brings a glass of water from well 7.......the knight bring a glass of plain water(not poisoned)

the dragon drinks this water, then goes to well 7 to save himself...but ends up poisoning himself he is not already poisoned.

the knight has already drunk from well 1, so when he drinks the water form the dragon, he is actually curing himself...

Sir M has it!

That was kinda easy, so I'll give the other half: Can the dragon ever kill the knight, assuming the knight is prepared?  Can the knight ever slay the dragon, assuming the dragon is prepared?

That sounds very plausible, but just in case:

Do the knight and dragon drink one glass each (including before the duel)?

Does the knight drink a poisoned water?

Does the dragon drink a poisoned water?

Did the knight win the battle fair (without the dragon dying from the poison)?

By "If you drink from a well, you can only save yourself by drinking from a higher numbered well", do you mean a higher numbered well than the one they just got poisoned by, or is well 7 the only antidote?

Did either of them add anything into each other's drinks?

Can dragons drink?

Could "After the duel, the knight lives and the dragon dies." mean that the knight lived immediately following the end of the duel because he had a slower acting poison (or just fairly killed the dragon); but afterwards the knight died?

Were they only allowed to bring one glass each?

Was it like cards where after kings, usually being the highest, you go back down to aces; so that if the man drank from well 7 he could be cured by well 1?

Did any of the wells run dry?

Did the knight have any secret antidotes?

Did the knight have water from well 7 from any previous situation?

Had the knight built up an immunity to the poisons by drinking just a little bit more each day?

Ohh, wow, that scared me! Congratulations

oh boy.....judging by the  above questions.....we have a , yet another, serious riddle contender......

i'm screwed.

Just trying every possible solution. I had no clue he'd be on right now... lol.

sometimes things move quickly.......

regardless.......that is the sign of a good riddler........lots of good questions..

(which hopefully allow me to figure it out first.......hasn't quite worked out that way for me so far.....but just wait..)

I don't want to even try to stab at the second half, it seems as though you'd be able to include any random happenstance as proof for why they could kill each other eg. "If the dragon was prepared, but it was raining, the knight would be able to kill him because his firebreathing powers would be severely hindered"

Also, where is this 'non-poisoned water' from? Even if they're on an island, unless it's on a lake, he would get nausea at the very least from drinking a glass of salt-water

I guess there could have been a spring or freshwater river flowing through it if the island was big enough... I mean, they would have to get their daily water from somewhere, wouldn't they?

Is this being terribly over-anylitical, or is this normal? Starting to doubt myself

Is this being terribly over-anylitical, or is this normal? Starting to doubt myself

I'd say you're going to fit right in here. Whether that means you're being over-analytical or not, I leave up to you 

yeah....i have to agree.

if i was the knight i'd hire the A-Team......that'll sort out that pesky dragon.

I'd say the dragon's access to well 7 would be a fairly unassailable advantage if they're both well prepared...

Would take more thinking to actually prove that though...

Depends on the situation - how many "actions" (drinking from wells, collecting glasses of water etc) do they each get? If they're in the process of being poisoned, do they know? Too many variables...

what would happen if you mixed an equal amount of water from each well and drank that?

I would guess that, depending on which order the half-glases were drunk (assuming that each different well's water would be of different densities, therefore seperating into layers while mixed), you'd either get poisoned with no chance of survival or you'd get poisoned and become immediately cured...

But anyways, I would say that if the dragon had the knowledge that he didn't drink poisoned water he could have the upper hand by planning ahead. I think that this would go on infenately as they trade back and forth. In this example, I guess the knight was just lucky.

But, by 'duel', do you mean that they fought, or the drinking poison mental duel? I based my above answers thinking that there was an actual fight taking place afterwards...

We're not given any information on their respective fighting ability, so I assumed the "duel" was just the strategy and mind games of the water drinking thing.

Makes sense. Well, if the second part is a question of physical dueling, I'm putting my money on the dragon.

Thinking some more, from the dragon's perspective, whatever poison the knight gives him, he can counteract it with well 7, but if the knight gives him plain water then he'd be poisoning himself by drinking from any well. In the event that he poisons himself (because the knight gave him good water) then he could possibly still save himself with well 7's water, but if he was poisoned by the knight then he's screwed himself over again.

I don't see any way around this... the original puzzle's solution works based on the possibility of serving up plain water, which we hadn't considered before, but with that out in the open the puzzle becomes somewhat intractable.

It's the same from the knight's perspective, but he doesn't have access to well 7, and would be caught between the possibility that the dragon might offer up poison (in which case he should drink from well 1 as above) or that the dragon might offer up plain water, in which case he shouldn't.

All comes down to whether they can tell if they've been poisoned or not, but if they can do that then the original puzzle wouldn't work.

"That was kinda easy, so I'll give the other half: Can the dragon ever kill the knight, assuming the knight is prepared?  Can the knight ever slay the dragon, assuming the dragon is prepared?"

I think I understand it better now. We're assuming that the dragon knows that the knight tried/ will try to trick him if the dragon is prepared. The other part about the knight doesn't make much sense, unless you wanted to use quadruple negatives. Assuming that you aren't talking about the situation Monty figured out, then that would mean the the knight being prepared is:
     1) The knight is going to trick him
     2) The dragon knows he will try to trick him
     3) The dragon attempts to trick the knight
     4) The knight knows that the dragon will try to trick him, based on all of the knowledge above.
     5) The knight somehow doesn't have a brain aneurism and figures out how to kill him*

I'd say that it would be impossible to determine for the simple reason that the knight or the dragon could be using reverse-reverse-reverse-reverse-reverse psychology at any time.

I think the correct answer to the second part is, based on luck of the draw (almost literally speaking), either one could win/lose.

*That would be something like:
The dragon brings a non-poisoned glass of water to give to the knight
The knight knows that it isn't poisoned and therefore doesn't have to do anything (In this situation, since he knows the water will not be poisoned [since he was prepared], he does NOT drink well 1's water before exchanging glasses)
The knight can now bring any water from any well because the dragon thinks that the knight will trick him by bringing non-poisoned water
The dragon thinks that he wasn't poisoned and therefore doesn't drink out of any well.

Nevermind, I might aswell figure out the other part...
If the dragon was prepared, then:
The dragon would know the water was not going to be poisoned
The dragon brings non-poisoned water so the knight dies from the water from well 1 that he drank previously

So basically, whoever was 'prepared', as you explain it, would be sort of.... well, prepared and always win, by default. I think you just added on that part to confuse us/ make us to more work to feel worthy

this is an excellent riddle with a good answer. me likey

I like the first part; the second part sent me into conniptions!

Maybe I should start answering questions:

how many "actions" (drinking from wells, collecting glasses of water etc) do they each get? as many as they want

If they're in the process of being poisoned, do they know?   no. drinking from a poisoned well tastes/feels the same as drinking from the tap.

what would happen if you mixed an equal amount of water from each well and drank that? can't happen

But, by 'duel', do you mean that they fought, or the drinking poison mental duel? drinking poison mental duel

The second part is asking "If both of the knight and the dragon are infinitely clever, can the knight kill the dragon?  Can the dragon kill the knight?"

Ohh! Thanks... makes uhh... more sense.
If both were infinately clever, they'd have the same amount of cleverness and no upper hand, meaning they would draw everytime. Right?

if one of them were to drink a glass from well 1, immediately followed by a glass from well 2, immediately followed by a glass from well 3...what would happen?

would the 2 cancel out the 1 and then the 3 poison them?

or would the 3 cancel out the 1 and 2?

Drinking every well in order:

Starting from no poison: drinks from 1, is poisoned.  Drinks from 2, is no longer poisoned. Drinks from 3, is poisoned....... drinks from 6, is no longer poisoned, drinks from 7, is poisoned

starting from poisoned from Well 1: drinks from 1, has no effect.  Drinks from 2, is no longer poisoned. Drinks from 3, is poisoned....... drinks from 6, is no longer poisoned, drinks from 7, is poisoned

starting from poisoned from Well 2: drinks from 1, has no effect.  Drinks from 2, has no effect. Drinks from 3, is no longer poisoned....... drinks from 6, is poisoned, drinks from 7, is no longer poisoned

starting from poisoned from Well 3: drinks from 2, has no effect. Drinks from 3 has no effect.  Drinks from 4, is no longer poisoned .... drinks from 6, is no longer poisoned, drinks from 7, is poisoned

...

starting from poisoned from Well 7: no wells have any effect. *dies*

so would i be right in say that whatever the knight gave the dragon to drink, as long as the dragon drank twice from well 6 and once from well 7, he'd be ok?

yes

if it is poison from 1-5, the first 6 cures it, and the second is a poison, which the 7 cures

if it is poison from 6, the first and the second 6 will have no effect - she is still poisoned, which the 7 cures

if it is not poison, the first 6 is a poison, and the second 6 will have no effect - she remains poisoned, and is cured by 7

So a clever dragon is unbeatable. Bad news for the knight...

ha!....bring on the dragon....i'll sort it out!

Now how about a clever knight?

yep...that's me..

How can you survive being given a glass of water by the dragon? (this includes water from well 7)

don't drink it!

always drink from 1 first....then drink a 1 followed by a 2 afterwards

Yeah... that works. Drink from 1 first and if the dragon brings you poison from 2 upwards, its negated, then you drink 1 + 2 and it works out ok

If he brings you water from well 1, you drink from 1 three times then from 2, no poisoning.

If he brings you fresh water, 1 + 1 + 2 = not poisoned.

Pretty crappy duel then, with proper thought about it, no-one ever loses.

they'd be better off doing rock, paper, scissors.

but what happens if you get thirsty?

The knight had somewhere to get non-poisoned water for the solution to the first part, or you can drink from a low numbered well then a higher numbered well.

For completeness, we can say that mixing water from two different wells produces clean water - the higher one neutralizes the lower one.

Continuing that, we'll say that mixing three different wells produces water identical to water from one of the wells, based on mixing order. (using wells 1,2, and 3)

Mixing order -> result
1,2,3 -> 3
1,3,2 -> 2
2,1,3 -> neutral
2,3,1 -> 1
3,1,2 -> 3
3,2,1 -> 3

Good lord... this is still going?!

shouldn't be...

LOL! Exactly.....

... oops, my bad.  Sir M has part two also.

+1 to Sir M

wayhay!

wow....that sure took a long time.......

well.....i was waiting for you to solve it.....

hah!

you would have been waiting a long time....

....i've never been knighted......apparently you are the only one here qualified to solve this riddle....