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 Alex Bellos: So this is one of Dudeney's famous puzzles, which, you know, still making money to the carpenters of Greece, but there's another one which is probably my preferred puzzle of his. And I've given this puzzle to loads of people. In fact, sometimes I've given them to like, professors... There's some really smart people, and it's not totally obvious how to do it. And this is a Dudeney puzzle... It's very very simple. All you need is... Six. One, two, three, four, five... Six coins. And, the idea is to get them into the hexagon like that. That's what you're aiming to get... And you must start from this. Okay? And the single rule is that you can move something anywhere by sliding, so you can't pick it up, just by sliding anything you move you can only put somewhere that touches two other coins. So, you couldn't move this to he- to- we could- to here. You couldn't do that because it's not moving to a p-- it's not touching two other coins. So this one here, you can move it to there, you could move it to here, You could move it to here... It just has to be touching two other coins. and what I want, I want you to get from there to... here, in three moves. You can do it in 4 or 5 moves pretty much straight away, but to get it in three moves, Does take a bit of thought, does take a bit of thought. And, quite often you forget how to do it, so you could be on another train journey and get it out, and... This puzzle here was really the beginning of... There are lots of other in the genre of, you've got a certain amount of coins, they're in one pattern, you've got to make another pattern, and you can only do it by sliding it to a place that's touching two others. What you don't want to do, is lots of people start like this: they think, "Well, I can do this, but then this one's trapped." Because you can't move that one out because these two are doing it. So you- you've gotta- And you can't take it up. So you can only do it by sliding, and you're not allowed to move any others. So, the way that you would solve it, if I could just remember how on earth I did it, is... Yeah, you put- No you don't... [Chuckles] This is hilarious. I haven't done this in a while, and I say the reason why I really enjoyed this puzzle is that you You forget -- I'm gonna find it, I'm gonna find it, I'm gonna find it. Brady Haran: I know! Alex: This is like stage fright this one goes here this one goes here. And that one goes there. I just assumed people were doing this for hundreds of years or that there was no kind of someone actually it had to go and invent it but Like so many other puzzles this one was invented by a Henry Ernest Dudeney. most puzzles try and - well, most mathematical and logical puzzles try and express some mathematical ideal to give you some insight and there have been some puzzles that I have invented to try and Express some mathematical idea which I've not seen before but what I also have done Which is what every puzzle writer has been doing since the beginning is That you have to rewrite and adapt all the old puzzles for a new age so You know I think the interesting thing about puzzles is that we've been doing pretty much the same puzzles for last 2,000 years And a good puzzle is something that that goes viral people want to share people want to Either ask how to do it or they want to see if the other person is as clever as you And this is something that with the Internet has really shown that and I first started writing about puzzles when I realized how viral they could go and as I researched it I Realized that every puzzle that I was reading from someone was actually a rewritten puzzle from someone else And then you can kind of trace it back so being a journalists really by profession in the vein of "Can you solve my problems?" I try to sort of tell the history of how these things work, and it's a little bit like jokes so jokes you know It's not often that someone actually invents a whole new joke. Essentially what they're doing is they're retelling that joke. You know with the few new words in it, and the intonation is a bit different puzzles are exactly the same that they are They're like a living thing and they can they carry on going and they get better in the retelling Brady: Hi there everyone, thanks for watching do you have a coin to hand? If so, Why don't you toss it, if it comes up heads, click on the left for our coin playlist. And if it comes up tails, click on the right That's an objectivity video about a whole box of puzzles featuring Matt Parker so these are very much loose papers [Oh!] exactly as they were presented to the Royal Society So there's a lot of very miscellaneous material in here Brady: if you haven't got a coin Well just choose, I guess
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# The Coin Hexagon - Numberphile

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