Can You Guess Who's Lying? 3 Logic Riddles to Train Your Problem Solving Skills
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- čas přidán 26. 08. 2018
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Now I‘m wondering what it must be like to live on this island.
haha
Well, if you grow up there you know who's who and it'll come naturally to always believe something else than what knaves tell you, I don't think it'd be too hard.
fake news
Imagine being a knave =( just a bad time
In Japan, language is gendered. Men and women use different words to refer to the same thing. But Japanese people get used to it. If you grew up on this island, you would learn that "no" means "yes" for exactly half the population, and get used to it.
Would I like more videos like this? I whispered my answer to the guy next to me. Ask him...
He's a knight and said YES please!
@@amphibiousone7972 are you a knave though? *plot thickens*
@@adolfomotanavarro6553 giggles
Knights will answer yes to this question. Knaves will lie and say no.
They are either both knights, or both knaves. Since it's CZcams, I'm going to assume they're knaves.
@@jacobcain9008 Unless you're a knave and lying about CZcams. The plot thickens
So, I made a chart, 4 possibilities:
B | B
---------
K | K
K | K
K | K
K | K
...oh, their names start with the same letter and the types of people too! I hate these kind of riddles.
But great video
Jakub Homola I was trying to do the same until I realized that xD
I just did it with T(true) and L
Now that's funny! Cool😉😊😂
Okkk
Jakub Homola There are only 4 different types of possibilities in this which are:
Knave:Knave
Knight:Knight
Knave:Knight
Knight:Knave
There is a whole book of similar puzzles, getting progressively harder, in Raymond Smullyan's book "What is the name of this book" . He was a professor of logics and wrote a whole host of popular books on the subject in the 1970s and 1980s. The irreplaceable Martin Gardner, who wrote for Scientific American, had some excellent pieces on the truth teller/liar problem as well which are in his various "mathematical puzzles and other diversions " series of books.
The second riddle is just a bunch of buffers and NOT gates in series
EXACTLY what I thought of! :)
A fellow IT guy
for a moment I thought that you were stating that they are not gates in a series...
I feel 😂 Took me ten seconds to go: "oh okay, so they said 'No'." Then it took me ten minutes to realize the significance of phrasing the question as a hypothetical.
Haha you're right, the knaves are NOT gates and the knights are buffers, that sure makes it easier!
5:32 "Now, we can't just brute force like we did in our last example..."
I just wrote a program to brute force it.
@Lord Colin Yeah, Essentially Knights are buffers and Knaves are inverters. You know you have 5 buffers and 5 inverters, you just don't know what the first one is, but you have the resulting output, so determining the unknown is trivial.
Sounds like something a knave would say...
Another way to solve the last one, realise that if one statement is true then all to the left are true. Then 5th is the highest one where what they say doesn't contradict this fact.
Wow
Somerandomdude4.2526 Actually only one is a knight. Because only one can have the right answer. Yet they all had different answers. Meaning one knight because 5 knights would have all answered the question the same. In order to tell the truth.
Knights always tell the truth. Evidently, they don't always tell the *whole* truth.
That, or you're having trouble with "at least N of us are X" being the same as "our group contains N or more X" or "the number of X in our group is greater than or equal to N"
WOW, you are a natural😄 and....oh heck, just WOW
thats the way i did it
I don't understand why a knave would answer no if I ask "If I asked you if you were a knight...", shouldn't it also be yes?. Anyway, loved your riddles and love your videos.
Skeith M. Even, I've doubts about that.....
It's because there are actually 2 questions in the question, so a knave will have to lie about both questions. Since the first question feeds into the second question, the answer to the second question ends up being a double negative, which makes it true.
Or another way of thinking about it...
If you asked anyone on that island if they were a knight, they would of course answer yes.
But then if you immediately follow with another question where you ask what answer they just gave, a knight will tell you the truth and say yes, but a knave will lie and say no.
So the question "If I asked you if you were a knight, what would you say?" is just a way of combining those 2 questions into one question.
@@W4LL37SK83R yeah, it arises from the premise that a liar is not attempting to mislead, but strictly constrained to say the exact opposite of the truth. Are you a liar - no. If I were to ask you if you are a liar what would you say - yes. The second answer depends on the idea that the liar behaves with strict integrity, rather than seeking to mislead.
Thanks for the explanation! As a not native speaker it really didn't made sense to me why would the first say 'no'. I feel it is not really a logic problem but a linguistic.
ooh, I get it now! Thank you :)
This was a lot of fun, and it's amusing how even when not discussing physics, you still use its vocabulary.
haha I didn't even notice!
Up and ATOM I didn't notice LOL
Know LOL from 1000000000000000000000000000000000000000000000000000000000secs ago
Up and ATOM is mad *runs while screaming*
What makes this so fun is the amazing narrative and animation. Top notch!
This was my one my of favorite videos in this channel.. I loved solving these riddles and it was really satisfying to be able to solve them :p Looking forward to more riddles Jade :D
With the fear that I may sound like a broken record, I still truthfully love these videos and think whatever format you do them in has been completely effective. Short answer: yes. Please do these if you so feel.
I LOVE logic, problem solving, and logic puzzles. Problem solving is a higher form of learning compared to memorization. And I don't mean that to sound biased. What I'm saying is that nearly everything anyone learns that they have to memorize was FIRST "solved" in a way to make those puzzle pieces fit correctly. Then, many simply memorize the pieces and how they fit.
For instance, in music, there are 12 major keys. And most musicians who read music memorize these. But there is a definite pattern (and rules) that you can apply to build any major scale from scratch. The seriously cool thing is that, once you "solve for" any particular scale, you come to realize WHY there are only certain keys that work well (like Bb and NOT A#). For that particular example, the very simple answer is the key of Bb has 2 flats: Bb and Eb. But the key of A# (which sounds exactly the same) has 4 sharps and 3 DOUBLE SHARPS!!! A#, B#, Cx, D#, E#, Fx, Gx!!!
So not only does learning to problem solve help to find (new) answers to problems, but it can help people to understand the nature of certain things that many simply take for granted.
You just made music sound so much more interesting to me than ever before lol
Thanks :)
Up and ATOM
what causes a key to have a specific number of sharps or flats?
A lot of DnD has taught me the most efficient way: murder hoboism - stab one of them. Then ask the other if the other is dead. Now you know
Good one..
You could just ask what color something is
What if it's Schrodinger's island, and the one you stabbed/didn't stab is BOTH alive AND dead?
you fucker, you totally didn't just stab me!
I have to say your wording is what confused me on question 2. I ended up rewording it and was able to solve through the same.
My original issue is I had the knight and knave both answering yes which tripped me up. After the correction our processes matched.
These Logic Riddles make me think harder & think of new ways to solve these problems. Please do more riddles like these Jade! :)
What a great video. I would definitely love more such riddle videos. Such awesome animation which makes learning more fun. I had great time trying and solving these riddles. These riddles really involved me a lot which I really liked. Keep making the good stuff and love your videos.
For some reason the hardest for me was the first riddle.
that's good it means you learnt and got better :)
Me too. I was certain about the answer and wanted to skip to the next riddle but then I saw Jade's result was different. My first thought "she must be wrong" did not seem so likely. I went back to watch the explanation only to realize that I understood the task wrong :/
Totally the same. Actually got the 3rd one at a glance.
Wreck really... because it was the wrong answer. Actually only one is a knight. Because only one can have the right answer. Yet they all had different answers to the same question. Meaning one knight because 5 knights would have all answered the question the same. In order to tell the truth.
Yes the first one is in many respects harder, it's the icebreaker helps you learn the rules....so to speak. Great job!
I really loved these riddles. Especially the second and third riddle ! Very innovative. Please make more videos like this
Jade, really liked this kind of video!!! I like your regular content because I always learn something, but more frequent uploads with riddles is fun too!! I think you should keep up with the two kinds of videos. As always, I like your content because you make me a better person video by video!! Thank you for all your effort!! Keep up the good job!!
For the last one you could solve it without stepping through every person: if N is the number of knaves, then there are also exactly N knights (those saying "there are at least n knaves" with n
Really fun riddles! thanks for the vid!
The hardest part in the riddles for me was to realise that the negativity propagate through all the statements(and so you could use double negativity to always have the truth) as in boolean algebra. For some reason I assume it only work one time.
Loved the video. I tried solving all the 3 problems. In the middle one, I got stuck for some time. Then I solved it using boolean logic (like considering Knight as 1, Knave as 0 and the answer YES as 1, NO as 0 and then questioning someone if the answer is YES is XNOR operation). It was fun. Will be waiting for your next video :)
Like, i found your channel today, the vid u colaborated w diana, and i binge watched ur videos, and you gave me one extra video the same day??? Lol love it
welcome!
@@upandatom oh i forgot to mention that i did subscribe obviosly! Great content and intresting topics! Love your work!
Do more of this! Just got to know your channel and I love it!
Kinda reminds me of the math behind transistors that confirm or negate an input and thereby perform the kinds of calculations that let me watch your videos. I bet Alan Turing would have loved your riddles
YESSSS!!!! Definitely want more videos like this. It was an awesome video .
Super simple explanation for the second one. Anytime you have 2 options and there is something that flips the options (knave lying) the the odd number will always be the wrong answer and the even will always be the right answer. Best analogy I can think of is gears. One gear will turn counter clockwise, two gears will result in a clockwise rotation, three gears will result in a counter clockwise output, etc. Any situation will follow that pattern, odd is unchanged even is changed.
Love your videos. Also keep doing videos like this once in a while.
That was fun! I saw the third one immediately by going back and forth between the first and the last ones so that one was pretty cool! The first one was easy to solve your way through, but the way you asked the question in the second one threw me at first. Amazing video, I learned a bit about logic.
Subhasish Mukherjee Funny considering the third one was wrong. Actually only one is a knight. Because only one can have the right answer. Yet they all had different answers. Meaning one knight because 5 knights would have all answered the question the same. In order to tell the truth.
@@ericknyevz3840 they didnt say an exact number, they all said ***at least*** X, so that allows for up to X to be telling the truth.
its definitely the easier one since once you eliminate the possibility that all 10 are knaves or knights, the only logical solution would be half/half.
If they said "only X of us are knaves" that would be true, and the ninth person would be right - only one answer can be right since they all require different numbers of knaves. It cannot be the last one since they cannot be a knight if all of them are knaves, but if the ninth person is a knight so there are nine knaves just like they said, meaning this is the only answer that can work.
This is also not the actual answer as they said "at least X of us", which the comment above me already said, but ai wanted to experiment to see "what if?" Although it was even easier, it was nice.
This made me miss the Professor Layton games I used to play on the DS, with the riddles. Great stuff, really enjoyed pushing my brain!
LOVE THIS VIDEO SOOO MUCH!!
I really enjoy watching your videos
Plz make more riddle videos
Thank you
The third riddle reminded me of the challenge "Sum the integers from 1 to 100" in that pairing the ends of each series makes the question clearer.
You've the coolest videos in CZcams related to the scientific stuff presented in the coolest ways possible! I'm pretty sure that I am the biggest fan of your channel! I remember you have a book on algorithms applied to real life scenarios, could you please make a video about some of the cooler algorithms in the book?
Forever a fan! Thanks for the awesome work.
sure coming up!
Excellent books for these kinds are the famous Raymond Smullyan books like :
What Is the Name of This Book? The Riddle of Dracula and Other Logical Puzzles
The Lady or the Tiger?
To Mock a Mockingbird...
and so on.. he does a LOT of knave-knight puzzles.
Amazing books! If I remember correctly he even proves Goedel's theorems using similar stuff.
Love the videos.
Thanks for posting them.
My 10 year old has come up with an innocent solution to this riddle, which is to just ask a simple question to an islander "what is 2+2?" lol
Billy whispers his answer to Bob, and you have to ask Bob what Billy said. Sadly it makes no difference what question ask Billy!
The 3rd one was really good as l learnt something new. Thanx Jade
Hey I chose the exact same approaches on the first two like you did :D Except I imagined the second one representing knights as multiplying with +1 and knaves as multiplying with -1 so the result would be (+1)^5*(-1)^5=-1 which is basically the same like you did. The last one then was just iterating until no conflict :)
Cheers to your channel, very cool videos!
This actually broadened my thought process!!
Yes, more of problem solving videos. I'm sure many people do want to watch such brain teasing stuff presented in an interesting manner
So Fun! My thought process on the last one differed, focusing only on the 5th and 6th islanders, but was still valid. Thanks so much for this video and your channel :)
@@physicslover4951 umm... ? I don't understand the point of this comment.
@@dustincousins Nvm :/
@@physicslover4951 hope I didn't offend. I really didn't get it. I don't understand many social cues. Cheers!
@@dustincousins I wasn't offended. Even I felt kinda weird re-reading my reply. Sometimes I do things that are meaningless, it's nothing new...
Love your videos! Better than coffee to wake up the brain!
I loved this sooo much!
Hey, I really liked the video!
Generally I did came up with the first step or two of each riddle, but since I'm watching these in my comfort zone, i.e. Bed, couch ect..
I'd prefer a noo need to write down kind of riddle..
Maybe it's just me..
I do miss more of your modern physics vids, I'm actually an engineering student, but you bring a bright perspective to it.. Love it ^^
Keep up with the goodies :)
9:07 The first one being a knave would say "yes" since the truth is "no"".
This goes for any case where a knave is asked "Are you a knight", but
you can check that if you have both a knight and a knave.
You ask the first one "are you both knights", and he then must whisper in your ear.
Then you ask the second "are you both knights", and he then must whisper in ur ear as well.
Th one that says "yes" is the knave, for the answer is "no"
The first one was easy; I used logic tables to solve the second (EXOR and EXNOR), and I proceeded linearly from the first guy in the third(rather than oscillating between the last and first). Anyway, I love this!
For the last one, however, I initially correctly guessed 5, due to the symmetry involved.
Love it! Bring it on!
Loved the video! :D
Thanks for the episode; those were fun games!
Good old classics. Great Video keep doing your thing. Nice intro to problem solving. As always Thank You. I send young minds to you, because I know you are a great bigger sister type, and my fellows in here seem to be conscientious and respectful . Great room for exploation. 😄Thanks to everyone!
on the 2nd riddle at the end when you ask the knave if he was a knight he said no, but as a knave lie and say yes
Michael Harmon You didn’t ask him if he is a knight. You ask him if you would ask him if he’s a knight, what would he answer. Note that this is a subtle difference. If the first person would answer directly instead of whispering, here’s how a conversation would go if he’s a knave:
You: if I would ask you if you’re a knight, what would you answer?
Knave: No.
You: Are you a knight?
Knave: Yes.
See how in the first question (which is actually two questions nested in one) the person would lie about the lie he we would tell about being a knight.
I had to watch it a few times to get the difference. I finally worked it out by re-wording what each question is ultimately trying to answer. Question 1: Identify yourself, Knight or Knave. Question 2: Identify the answer to the question “Are you a Knight”, Yes? Or No?
I got em all! I usually don’t like pausing to solve on videos like this, but I tried this time and got them.
love your channel!
Enjoyed watching your videos
Love it, going to watch it tomorrow, sober :-).
Very good riddles. I liked a lot.
Nice work Jade
Omg! This is so amazing.
Loooved this😍
I have given my strong response Jade keep the good work☺️👍
I just like listening to Jade's voice. I tuned out that knight/knave stuff at around the 0:45 mark.
Jade... there seems to be a problem here at 8:01 -- If you ask a knave if they're a knight they will also answer "yes". So the question of "Are you a knight" returns "yes" in both scenarios.
i fumbled the first one, but once it was explained, i got the second 2! great vid
Did you draw everything yourself that is in your video? Your videos are impressive. Thanks for making them.
watching this when first waking up is a bad idea, now I know how my PC feels when I do too much at once.
Up and Atom covers such a broad range of topics. I love it.
Really love this video. Made me think very hard .... 😃
Scenario 1: Let's assume Billy is a knave and Bob is a knight. You go up to them and ask your question. Billy whispers to Bob: "Should I tell her?", but before Bob answers, you ask your second question. Bob answers truthfully (as knights do), but you still come to the incorrect conclusion.
dang....only got the last one.....but, that means that I learned from your lesson, which was the entire point! Thank you to you and your crew for your excellent work!
The 'Two Doors To Freedom' principle is another interesting one. It also uses the liar/truth teller approach. It can be used by the magician as a methodology to narrow down from four variables to the one with three questions or from three variables to one with just two questions. Works 100% unlike the 'Monty Hall' paradox.
thanks for pointing that one out, its also fun. but the monty hall problem isnt a paradox its just a statistical problem.
You can count on knives to make a sandwich.
Thank you for the video! All of you friends are super awesome! Oh, moments in this video are sad.
Only been following for a week but I fell in love with it during the first video.
lOVE YOUR VIDEOS JADE :)
Nice video to start my first day back to school.
The cute and funny animation always makes me smile.
In the second problem i found first that the second persons input was no but i didnt get the first question and ended up in a russels paradox
Fun problem set!
In the second scenario, when you ask the first person, "Are you a Knight?", his answer will always be "Yes.". If he's a Knight, he will be truthful and say "Yes.". If he is a Knave, he will lie and say "Yes.". But you said that the Knave would say "No."!
she didn't ask the question "Are you a knight?" She asked the approximate question "Would you say you were a knight?" This forces the knave to lie about what they would say, not about whether they are a knight.
I know the first riddle like this: you want to travel to the land of the Knights. There's a crossing, guarded by two people. One direction is to certain death (Knave Land), the other to the Knight's Land. You know the two either always lie, or always tell the truth. What question do you have to ask to get the proper direction to the Land of Knights? (you get one chance, your life depends on it!)
What helps me a lot with problem solving is to reduce the problem, e.g. 2nd problem:
1) You identified that knights always prpagate the answer. So the original scenario is equivalent to a scenario of one dude followed by 5 knaves, since we can remove all the knights without changing the outcome.
2) You also identified that knaves flip the answer. Flipping the answer twice gives you the original answer, so you can remove pairs of knaves without affecting the outcome. Hence the original scenario is equivalent to a scenario with one dude followed by one knave.
3) Because we know the knave flips the answer, the original problem can be reduced to a problem where there's only the one dude, and he answers "no". And that's a much more digestable problem size ;-)
I loved it !
I thought this was 7 second riddles. Now that I know its you...
*RUNS TO COMPUTER xD* When you upload, I watch.
Btw I'm also the worst at problem solving :P
haha it just takes practice! I don't think I'm a strong problem solver either but I learnt some tricks and ways of thinking during my undergrad. Keep trying!
love your videos
Great fun, I enjoyed that. Apart from misspelling propagate.
So glad I picked this video to wake up to before a test!
I think there was a mistake at 8.12 asking a knave " if I asked if you were a knight" would not give starting answer..... no
Loved it
n_n
Love your videos Jade.(And you, You are the best explainer there is).
Indian?
I thought the last one was easy until in the explanation I realized they said AT LEAST. I took it as definite.
My head hurts but I’ll suffer it if Jade’s teaching me ❤❤
Ok everyone, I got 0/3.
How did everybody else do?
Same. I immediately thought of parity checking, but couldn't make any connection.
2/3
The more important question is are you a knight or a knave?
3 for 3, np
I misunderstood the first question of the first problem as the islander being asked of his own status, and hence got it all wrong.
In the second problem I realized that knaves would alternate the answer and knights would propagate the answer, but interpreted the question asked to the first guy as always giving the same answer no matter their status.
The third problem I got right.
Had an interesting think about the third riddle; it works for an even number of people but becomes paradoxical if you try to solve it for an odd number.
Take a simplified case of 3 islanders:
1: At least one of us is a knave.
2: At least two of us are knaves.
3: At least three of us are knaves.
Using the video logic, we can conclude the first should be a knight, and the third a knave. However, looking at the middle islander:
If they were a knave, then there are two knaves, so the statement becomes true, which is impossible for a knave.
If they were a knight, then there is only one knave, so the statement is false, which is impossible for a knight.
They're stuck in some paradoxical quantum knight/knave state where the only answer is that they're probably some dude who doesn't belong on the island to start with.
4th riddle: You find 2 caves in front of which are 2 people. All you know is that one is a knight and one is a knave. You also know that one cave leads you safely out and the other is a dangerous cave with no way out. You are allowed to ask only one guy only one question. If you try to ask for the second, the knave will kill you. What will you ask to find out the safe passage?
Another way to solve the last question is that the 9th person says that there are at least 9 knaves and the 9th person itself is a knight.
like it! you always come up with funny names. haha
Another way to solve the first problem is to reduce it to one question: "Would Billy call you a knave?". We never hear the answer to any question directly about Bob, so it makes the most sense to solve the problem starting from what Billy could be. If he were a knight, he'd tell the truth, so if he said "yes" Bob would be a knave and claim Billy would say "no", and if Billy said "no", Bob would be a knight and be truthful about what Billy said, and vice versa if Billy were a knave.
And I figured the first guy in the last problem was a knight right off the bat because if they were a knave, it'd verify their own claim. That leads to the problem being solvable from the opposite end.
I was sooo reluctant to have a go but I'd actually attempted and solved the third!
Another way to solve last one:
Assume there are (x) number of knaves therefore (10-x) number of knights
From person 1 to (x) all are saying truth therefore they must be knights so (x)=10-(x)
therefore (x)=5
Your popularity acceleration is great !
Wow
I liked it 👌👌👌