Can you solve the vampire hunter riddle? - Dan Finkel

You’re a vampire hunter entering the enemy’s lair. Can you outsmart this tricky brainteaser and vanquish the vampires?
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You’ve stealthily descended into the darkness of a vampire cave, setting a sequence of mirrors as you go. When the sun reaches the right angle in the sky, a beam of light will ricochet along the mirrors, strike a diffuser, and illuminate the great chamber where the vampires sleep. Can you place the diffuser correctly and flood the lair with sunlight? Dan Finkel shows how.
Lesson by Dan Finkel, directed by Artrake Studio.
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[@cicada.and.pomegranate]

this is basically the DVD screensaver as a riddle

[@leos9378]

Yep

[@myrafoundation3369]

Ikr

[@skychief1306]

Why is that so accurate

[@torchuga]

Henry's BS TV I was gonna say that.

[@jamiecasimir5040]

True

[@Rose-ez9vf]

Mufasa: “Any point the light touches will be even or odd” Simba: “what”

[@plasmablizzardvampire6502]

nice on

[@Jeremy-ws9tv]

favorite comment ever

[@americantoastman7296]

Made me genuinely laugh, thanks!

[@Rose-ez9vf]

Aw thanks guys :)

[@0ostormo0]

i dont get it :(

[@matrixphijr]

Vampires: *Hate sunlight* Also vampires: *Build lair with perfectly smooth, metallic walls that infinitely reflect light*

[@miriga3927]

Really though, I thought they used cobblestone

[@tonyblake7569]

That would actually make sense. The only reason the sunlight reached there was the mirrors he placed on the way there so normally they don't have to worry about that. Since it gets no natural light they probably would use candles or torches so having walls like that would allow a few to light up the entire room.

[@Nikku4211]

If the vampires built the lair, why would they use coffins instead of beds? Yes, I know they're reanimated corpses, but they're reanimated, so wouldn't they want something more comfortable?

[@tina.tina1]

@@Nikku4211 because they only go out in the night, and even if some day-light go into their cave, they are still protected by their coffins

[@RyanGerhardtYimimoto]

@@Nikku4211 if you go by classic lore like Bram Stoker's Dracula, they can only rest in unholy earth of thier homeland or place of burial. Coffins are good for that.

[@darealmrman2266]

"There is no time to draw the line" "Let's draw a grid" Wait a damn minute...

[@zacharyshelton1336]

right? wtf... also, right after he explained some of the grid, I realized right after my answer was wrong and it is actually very simple to figure out. If he hadn't said the answer was a simple solution I probably could have guessed the right answer... that's why I'm mad. good riddle though reminds me of the DVD logo bouncing off the sides of a tv

[@ralphschraven339]

The grid is just there for visualization purposes. You could "draw" it in your head, or simply leave it out and explain the answer using parity to explain the same concept.

[@wobblyorbee279]

@@ralphschraven339 yes. exactly, you dont even have to draw the grid in your head, *you can just.*

[@Cobra97917]

Well you could have done all this before going there…

[@sxlproductions]

​@@Cobra97917 you know what else I could have done before going there or do it RIGHT THERE? Drawing a line that bounces across the walls

[@SKfilming]

"you only have minutes before the sun is in position" "alright. let me pull out a ruler and make a grid"

[@sheeloesreallycool]

*writing* Go back down sun, thanks. *continues*

[@senaahasan5182]

@The Gamist "What? Dude,I don't care if millions are dying from hypothermia,can you see what we're doing?"

[@nadian848]

Lol

[@JohnnytNatural]

No, he only needs to measure the length and width of the room and since its 49x78 he knows exactly which corner it should be

[@stressedbyamountainofbooks]

@@JohnnytNatural no he just need to wait the light and place diffuser on that place

[@LasTCursE69]

*Puts diffuser in the right spot* *Clouds block the sun* FML..

[@destroyerofworlds4663]

LOL

[@MrSasukeSusanoo]

You vampire food now

[@unicatpops473]

More like FMDL As for F**k my Dying Life

[@lightyagami6307]

🤣🤣🤣

[@ryanramjattan8714]

F

[@ABM_GD]

“The walls are covered in coffins” 10 seconds later “The light will bounce off the room’s perfectly smooth metallic walls” Hold up...

[@aldoorymahagoub3951]

The coffins are made of smooth metal to make sure no light enters the coffin and disturbs the vampires

[@three3ofspades610]

@@aldoorymahagoub3951 The problem is it gets uncomfortably hot in the summer, probably

[@aldoorymahagoub3951]

@MARTIN OLLO VAL the coffins are parts of the walls The wall is caved so you can perfectly place a coffin in the gaps

[@lisahenry20]

@@three3ofspades610 I don't think it would. The light is only entering the chamber because of the mirrors you've put in place. My grandad has a metal shed which is freezing cold the times I've been in there in the morning, so if the coffins work similarly, they will probably be even colder, since they would have been out of the sunlight for much longer than just a night.

[@javierlatorre480]

The way it's shown, the coffins cover only the bottom halves of the walls, and the light travels horizontally overhead

[@thekoolquintents6770]

People: " why do we have to learn angles?" Ted ed: "for vampire hunting silly!"

[@soeunj1108]

Tbh vampire hunting sounds more motivational it comes to studying

[@Alfwed]

We only have minutes before the sunlight reached the room. “Let’s draw a coordinate graph.”

[@Antonio_611]

every respectable vampire hunter has a grid paper in his pocket

[@ahmedal-saeedi5988]

Wellll tbf they were only showing u how it works with the grid 😅 Like you didn't need to draw anything to figure out the coordinates of the three points

[@studiousboy644]

I suppose you have no imaging capacity then? Also vampire hunters keep every mathematical tool.

[@ipizza9941]

It was just so we could understand, some people could have done it in seconds.

[@SylasTheGreat]

@@studiousboy644 Why so negative?

[@samnesium2003]

I honestly don't know why I keep watching these riddles. Every single one of these riddles I thought I could solve but then switched off my phone and felt dumber than ever.

[@pilotpuntastic6513]

These feel less like a riddles and more like intricate math problems framed to be mistaken for a riddle

[@ifyourereplyingtomycomment1941]

Yeah same here, they all involve math and I'm no good when it comes to math :')

[@brrmbrrmm]

i could relate,but was found shooketh when i realized i got this one correct i was like: hmmmm corners corners corners... so the light bounces at a whatever degree angle? okay... those other corners seem to be too far,ill just with south east bcuz my gut trusts it too and bam

[@lucania101710]

Yeah, these are math problems, not riddles

[@Arakasi22]

Don't put it up, have a vampire bite me and then live forever while vanquishing my enemies.

[@icantthinkofaname8139]

Walls: are crowded with coffins Also walls: perfectly reflective at every point

[@garvgupta3567]

the coffins are lower the diffuser is higher

[@yoursleepparalysisdemon1828]

“Strike your diffuser” Bruh that’s a disco ball

[@uttamdas5834]

Lol

[@thelorekeeper8839]

we're gonna kill them with the power of the 80s

[@funnytoad31]

It's homemade

[@InkWaxstudios100]

Isn’t that what disco balls are built to do?

[@yoursleepparalysisdemon1828]

@@InkWaxstudios100 thstd the joke

[@ninahuang6719]

step one: bring 3 diffusers step two: figure out why you look like a tomato

[@amirasad2012]

LOL Yeah

[@weirdnesslord8573]

I Rather Nuke The Whole Thing

[@PyroGothNerd]

Sunburn, maybe?

[@jeffgagstetter7713]

That’s what I did

[@sepiived]

Omg i died laughing when i read this XD

[@w.5655]

You have no time to spare _Let's draw the room in coordinates_

[@alilweeb7684]

I was thinking that

[@zerotolerance280]

Lmao true

[@vinayranga2211]

You don't need coordinates of the whole room, just the coordinates of the corners, which is given as you know the dimensions of the room.

[@memetic.trojan.objprime238]

Yeah this is actually pretty intuitive and simple, I solved it within 1 bathroom run.

[@jaynor9885]

@@alilweeb7684 oof ikr

[@PhantomSavage]

This is one of those things where you think the answer is actually really clever and out of the box, and in actuality its just a graph and math problem our vampire hunter manages to write out and completely solve in a "few short minutes"...

[@LucksackGames]

The thing that always shocks me is it feels like it would take more than just a few minutes to go ahead and draw that line haha, that he said you didn't have time for.

[@thisusedtobemyrealname7876]

Has only few minutes: "let me just draw this coordinate grid first."

[@LucksackGames]

@@thisusedtobemyrealname7876 You can't draw 281 logical solutions in 30 seconds? Me neither. Random guessing will be my default too!

[@gabriel7932]

@@thisusedtobemyrealname7876 the grid was for explanation

[@MarsJenkar]

The thing is that you don't actually need the grid to figure out the answer. It was just there for illustration. Once TED-Ed explained that a diagonal line would always travel through coordinates that were both even or both odd after it emerged from (0,0), I knew what the answer had to be given the dimensions of the room.

[@nocturnalkoala8870]

Step 1: confirm that the vampires have green eyes Step 2: let them live in peace

[@baloch78]

Nocturnal Koala 🤣

[@rafhaelgonzales3436]

finally a green eye comment could have been more funny in my opinion

[@vaivs7903]

Ok this is the second time i read a "green eyes" comment. Where does it come from?

[@rafhaelgonzales3436]

@@vaivs7903 its just another riddle from ted ed called the green eyes riddle.its referenced in every ted ed riddles

[@amountedak9246]

I have been rewatching a lot and im glad to see that this is now a thing.

[@jukkasaarinen35]

Finally, i can use math to count in what point does the dvd hit the corner

[@carlosibay3900]

Jukka Saarinen yes

[@parkerglenn9317]

This is the finest use of this knowledge ever conceived.

[@jacrooki9560]

An intellectual using internet culture and geometry

[@yvonnienatasha1010]

Intellectual.

[@pi17]

Oh you do remember those!!!

[@mohdsyafiqsapawi9190]

'You don't have lot of time...'' *Proceeds to drawing a coordinate graph*

[@nelsonnoname001]

Lmao Thank you! Yes

[@Richie_P]

I'm pretty sure the sun is going to rise again tomorrow, so you have as much time as you want.

[@nelsonnoname001]

Pretty sure you don't, you go into the lair min before sunrise, darrr darr

[@niquel5831]

Coordinate graph is just to illustrate how to reach the solution, you don't need it at all.

[@donttrustnoone3921]

Ikr

[@letsplaysquire3257]

"the light reflects off the smooth metallic walls" WTF! I don't even need this diffuser!

[@aprinnyonbreak1290]

Well. The vampires put all their coffins at points with 1 even coordinate and one odd coordinate, so it's fine. The light will never strike them unless it gets diffused somehow.

[@-Offstar]

"You only have minutes before the sun is in position" Proceeds to measure the entire room rounded to the closest meter, create a to scale grid of the room, and then figure out where the light will end up. Yeah seems quick, simple, and elegant to me.

[@tonyblake7569]

Went to city hall before and got the blueprints.

[@tina.tina1]

And you have a big chance to fail, because it will be possible to have all 3 corners with even numbers.

[@arcticdraco6560]

Also, he said that they "didn't have time" to do the EXACT SAME THING.

[@ltymchenko613]

By the time the light hits the disco ball, the light has basically already lit the whole room😂😂

[@Ebin-ix2jg]

Its a diffuser but disco ball will work i guess😂🌚

[@TheDreamLeaf]

I was thinking the exact same thing lol. Diffuser not necessary when vampires have a brain freeze and make their walls smooth metal

[@ikeandroy7]

@Motorsoul ss Il L L li

[@iluvmilktea3224]

True

[@buildertherobloxian4731]

But that’s before the Coffins are Open.

[@VladCodY]

there are 2 cool things about these clips: 1. the riddle itself 2. the comment section

[@alishayin4279]

And then you realize your comment is better than the riddle...

[@luchacha9428]

Problem, I’m in the comment section

[@lily-ts4tu]

@@alishayin4279 Now there are three cool things about these clips XD

[@alishayin4279]

@@lily-ts4tu lol

[@villagecommenter8262]

3. green eyes

[@sophiesmith9300]

"Alrighty gotta set these up for tomorrow morning" Vampires: Cool I guess we'll sleep at night then

[@omegastar2508]

They partied too hard and slept in

[@justinmontana3710]

I just wanna say that the animation of the light bouncing off the walls at the end is really satisfying

[@josephmanning2129]

Don’t worry, I got this. I’ve watched the DVD screensaver for hours on end.

[@tapio_m6861]

Like on the office

[@autumn4442]

@@tapio_m6861 Why do people always reference the office when someone mentions the DVD screensaver? Do most people only know of the DVD screensaver nowadays because of the office? I've never seen the office.

[@aditya95sriram]

@@autumn4442 kzbin.info/www/bejne/h4DXpotmn7Fra7s

[@CoolGuy-xm1wm]

Bet you didn't miss that ..🎶

[@Clandhad]

I was waiting for someone to say that

[@BobMcCoy]

*_Dracula has left the chat_*

[@JustADioWhosAHeroForFun]

Wanna play Overwatch?

[@Anthony-gx6ng]

But... But... But You could have made it the dvd saver riddle

[@JustADioWhosAHeroForFun]

@marios gianopoulos *better vampire than Dracula btw*

[@JustADioWhosAHeroForFun]

@marios gianopoulos u rite

[@sarahthegreat2593]

Bleh bleh bleh

[@kevinmoy3752]

Honestly thought the answer would be, "the walls already reflect the light infinitely in the description, so you dont even need the mirror"

[@tonyblake7569]

My thought is when it hits that corner it would bounce back the way it came so wouldn't keep on going.

[@kevinmoy3752]

@@tonyblake7569 That would be true for polarized light

[@amsi4087]

Finally, all those years watching the DVD logo boucing on the TV.

[@Macapta]

if the beam of light bounces around the room at so many different angles is there even a point to that diffuser? looks like the beam filled the whole room as it is lol

[@runasfastasyoucan]

That what I was thinking!

[@aMxx-]

Same

[@pj18tires8]

Yes you need it. Light will bounce around the room at so many different angles in less than 1 second before it exits through the southeast corner. Chances are it won’t hit any of the vampires as they will be barely getting out of their coffins.

[@TheLongBow]

He should have said ray of light

[@Sarah12471]

@@pj18tires8 wake them up first

[@kokodragostinovdragostinov8754]

Now I have the ultimate power to predict which corner the DvD screensaver will hit.

[@davep8282]

Haaaaaaaa! I was going to make a similar comment. I don't think that thing ever hit any corner!

[@johnsjunk9157]

haha

[@kruzerblade4740]

Lol nice

[@carltonblend]

WOW SO MANY LIKES

[@lizalaagan3088]

I have seen it hit after frickkin 2 hours of just watching it idk what i was thinking

[@dootdoodle569]

The room is covered with coffins The light perfectly bounces off the walls Where the muffin does the light bounce off of and why can’t I put the ball there?!

[@mgt7728]

If you were to put the ball on the side instead of the corner, the angle of the ball would not be the right angle because it is facing straight. But the riddle requires the ball to face 45 degrees.

[@jellytomlinson3850]

Actually I think he means that the coffins are stacked on the ground. To put the disco ball on the wall means crawling on the coffins.

[@swifttech3602]

Nobody: Lisa Lisa: lol imagine needing mirrors.

[@aprofessionalgamer5355]

?

[@swifttech3602]

@@aprofessionalgamer5355 i'm guessing u never watched jojo's bizzare adventure.

[@aprofessionalgamer5355]

@@swifttech3602 N I C E !

[@asterism343]

Aha! I knew it! I knew there would be JoJo reference somewhere around here.

[@user-qx2re7is1b]

No time at all draw a complex drawing Me:what the

[@fluffyface4449]

Wait I go into the vampire lair and set everything up in the middle of the night for the next morning. Wouldn’t they be awake at night.

[@autonomouscollective2599]

Bailey Davignon Yes. That’s definitely a plot hole.

[@isabeltoledo3951]

At night they would be awake

[@Amanda-rn6tw]

Yes yes they would

[@emmaleffler5944]

yep

[@florisbekke7754]

Well, they are going to notice all the mirrors hanging in the cave when they enter back?

[@ElliottDenizen]

If the entire room is metallic what is the purpose of the light diffuser? Shouldn't the the room glow with mirrors on all sides.

[@cisforcringe5645]

elliott diaz No. There were parts of the room that couldn't be touched by the sunlight.

[@dairypig]

SasswaterOceans yes, but vampires are not small enough to fit in them

[@shima_galera]

That's impossible, the metallic walls are covered by vampire coffins.

[@fancylamp_]

The light is not bright enough

[@natnew32]

The light only bounces at a specific height, presumably above their heads.

[@mchammer5026]

You can imagine this as, instead of light bouncing off the walls, repeating the room infinitely many times horizontally and vertically. To hit a corner, you must therefore make a square by repeating the room on each axis. Notice that 49 (= 7 * 7) and 78 (= 2 * 3 * 13) don't share any prime factors, so their least common multiple is their product. The light must therefore cross the room 49 times horizontally, and 78 times vertically to reach a corner. Since an odd number of crossings gets you to the other side, but an even number stays on the same side, the corner it hits will be on the same side vertically (78 is even) and on the opposite side horizontally (49 is odd), making it the south east corner.

[@bakerlee912]

This was my approach exactly. Think of it like the old game "snake"

[@simonc7221]

3:12 is the most satisfying thing ever

[@TV-gn9li]

yeah 😊

[@laxxayy]

Is it a reference to DVD screensaver meme?

[@weedfarmer5633]

same thing I first thought of

[@dingypt]

Yes, i was thinking the exact same thing!!

[@wariolandgoldpiramid]

Not a reference at all, it's just a typical math problem.

[@Selas81]

Yay I am like #100 on this comment

[@mangor8543]

This

[@stormysamreen7062]

How can the light entering from the SW corner bounce off the "perfectly smooth, metallic walls" if the walls are covered with coffins?

[@Green24152]

it comes in ABOVE the coffins, dingus

[@raahilkhan1004]

If the light comes from above the coffins then why is there a limit for the places u can put the diffuser

[@natz3284]

@@raahilkhan1004 they already said the hunter doesnt dare distueb the coffins i.e. climb them to reach the higher points of the walls presumably

[@raahilkhan1004]

@@natz3284 ahhh okay.

[@okaberintarou5219]

Wish he bought a ladder along, that'd save more time than the coordinate graph.

[@Tarean1997]

I'm a little late to the party, but I think I found another solution to this: Starting from any corner, the next time any corner will be hit is after the amount of squares traveled equals the smallest shared multiple (no idea if that is the correct English term) of the two lengths. Since the leghts do not share a divisor, it happens after 49x78 squares have been traveled, or after the entire longer side has been traveled 49 times and the shorter side 78 times. The short side is traveled an even number of times, so the beam will end up on the bottom where it started. But the longer side is traveled an odd number of times, which means the beam will switch sides from left to right. Result: it ends up in the bottom right. Can anyone confirm or was I just lucky?

[@sunilrampuria9339]

Yup, even I had solved it using this method. It's called "least common multiple" btw, although smallest shared multiple sounds cool.

[@euxiciusahuizotl8890]

"you got no time to spare" "Watch me, ZA WAZUDO!!" Pauses the video*

[@sunnnyyy.]

toki wo tomare

[@iamtheone-mt3bu]

I’ve literally been binge watching these.

[@HighlightDepot]

iamtheone 4456 yeah

[@Schwuffie96]

Yeah me too

[@-AdityarajPatil]

Me too kid

[@isobelstewart6554]

Same

[@lulcy789]

Yep. Yepyepeyp

[@doiu92]

This Riddle: * Exists * *The People Who Watched The DVD Screensaver: "Where have I seen this before?"*

[@ahanaroyc.1330]

Step 1: confirm you have green eyes Step 2: ask the vampires to leave

[@defectiveemeralds9093]

"But there's one insight that can unravel the riddle in almost no tume at all" *whips out coordinate graph and it took 2 minutes*

[@saumyashah7978]

Why not just flood the room with garlic?

[@tiantian329]

Nice joke, but I’m a smart aleck so I have to intervene. The video specifically says that the greatest *challenge* was to use mirrors to kill a vampire. The hunter probably did it as a dare or for fame.

[@jacobh.264]

Garlic repells not kills

[@adamzero_]

how else can you know your dvd is on? you need the screensaver

[@gearshift7174]

Sunlight burns not kills stakes kill

[@ianmeyermarietta4328]

Have you ever seen a Belmont use garlic

[@NewbyTon]

*_THE SUN IS A DEADLY LASER_*

[@thomasthetankengine2653]

Let's make a religion outta this

[@emiliaperkins]

🎶Not anymore there's a blanket 🎶

[@OrtinFargo]

Newby Ton oh ok

[@zra17713]

I see you're a man of culture as well...

[@tuesdaywithanh]

Now you can eat SUNLIGHT!

[@Ivanhoenn]

When he said it was simple and elegant I just thought he was going to say put it in the same corner where the light was coming through and you don't have to worry about angles

[@rafirosin]

The perfectly smooth metallic walls, against which are stacked all the coffins? so how exactly does the light bounce?

[@lancelindlelee7256]

1. What Vampire would build their walls with reflective surface. 2. By the time sunlight reaches the point, it would be severely weakened anyway.

[@puraasu]

1:37 Read rule 3. “The light will not get stuck in a loop, *dim* or get blocked by other objects in the room.”

[@hurktang]

@@puraasu yeah but the riddle also say "sun light" not laser. The light will travel a total distance of 5400m and bounce once on every 2m worth of wall. So if the light beam angle is 0.02122 degree the whole room will be illuminated. The angular size of the sun from earth is 0.53° so indeed (this i push my research too far lol), the room is all illuminated.

[@hammadibrahim39]

@@hurktang how did you get 5400 m (plus all the other numbers)? Just curious

[@hurktang]

@@hammadibrahim39 I figured the laser would bounce every 2m of north south wall so a total of 49 time. So it travel east to west 49 time 78m = 3822m. That the east to west travel, so you multiply by sin(45) = sqrt(2) . 3822*1.4142 = ~5405m.

[@handsomeharold4698]

the sun would stay at the good angle for a bit. and the speed of light is speed

[@porscheman998]

I never would have guessed that. I heard the announcer say “simple and elegant”. To me drawing a coordinate would not fall under the former category!

[@rhowenbelisario5780]

Lol. Same thought sis

[@grahampcharles]

You wouldn’t need to draw a coordinate grid - only to realize that odd, odd or even, even are the only possibilities. The narrator only presents the coordinate grid to explain this realization.

[@daerdevvyl4314]

Crow Okay, think of each number as “how far to the east are we” and “how far to the north are we”. So the spot where the sunlight comes in is (0,0) because it hasn’t gone anywhere. Now, it’s always going to be going diagonal. He showed this with a graph, but you can think of it with a chess or checkerboard. If you try it out, you’ll see that when you start out at (0,0) and always go diagonal the two numbers will always be both odd (you’ve gone an odd number north from the corner, but also an odd number east of the corner) or both numbers will be even. So when you look at the 3 corners, they’re NW: 0,49 This is because it’s 0 metres east of the starting point and 49 metres north. NE: 78,49 SE: 78,0 And remember, for the light to reach that spot both numbers have to be odd or both have to be even. So the SE corner is the only possibility.

[@yourmomisgay377]

😂😂😂

[@j.r.1210]

@@grahampcharles No one thinks of a room in terms of x,y coordinates without having a coordinate grid to map onto the room.

[@Zxymr]

The solution in the video is poor as it allows for the SW corner to be a valid solution; it isn't, only because it was not an option in the riddle. To prove that it will hit the SE and not the SW corner, you can just imagine the rooms mirroring themselves upwards and rightwards infinitely, forming a rectangular grid. Because the beam moves at a 45 degree angle, we know that the light beam will only touch the opposite corner of a square block. To solve this, we can exploit the fact that the length and width are integers, and find the lowest common multiple (LCM) of 78 and 49. The reason is because the first corner that the beam will hit after leaving (0, 0) is (LCM, LCM). The easiest way to find the LCM is to multiply them and to divide the result by the greatest common factor (GCF), which can be quickly calculated using Euclid's algorithm. Since 78 and 49 have no common factors, the LCM is 78 × 49 = 3822. The first corner the beam will hit is at (3822, 3822). At this point, the beam would have reflected horizontally (3822÷78)-1=48 times (even number), and vertically (3822÷49)-1=77 times (odd number). This means that its horizontal direction will not be flipped, but its vertical direction will be flipped. It will be moving rightwards and downwards, and will hit the SE corner first.

[@pinkythepinkslime6170]

The southeast corner is the entry point. Although this reasoning is perfectly valid!

[@Rbum4]

Pinky. West is left. The comment is right. I'm really disappointed in this riddle. The solution fully depends on the dimensions of the room, which are not given! It can be any of the other corners (given sides with integer lengths)

[@MsKeylas]

It actually doesn't ask in which of THREE mentioned corners, just in which corner so a southwest one is perfect

[@A_Wild_Dyzzy]

I feel like just drawing it on paper and sketching out a rough line would be faster than the option you just proposed. as proof, I did exactly that, and it took me less than 10 seconds to figure out the SE corner was the correct option.

[@chaskaconcar-tavares1358]

You could just stand in the center of the room facing the light with the defuser in your hand

[@archetype101]

Oh. THEN WHAT THE HECK DID I GET A DEGREE IN MATHEMATICS FOR?!?!

[@MiyuTheFallenAngel]

That’s exactly what I said XD

[@MichaelKondrashin]

@That one friend that genuinely enjoys Rick Astley all was are reflective ;)

[@AA-gw7hd]

Ye, but he says that the diffuser has to be wall mounted

[@MrSasukeSusanoo]

But if you're holding the difuser who will kill the vampires? You know that not all of them will die right? :v the strongest one almost never dies instantly, it will kill you before being ashes while you're holding the difuser

[@lemondragon18]

If the beam of light has to bounce off the walls that much just to reach the diffuser, wouldn't the room already be lit up with sunlight? You pretty much don't even need the diffuser. Also, unless the sun is emitting a perfect laser beam, there is no way a beam of sunlight is going to perfectly bounce off the room's walls that much before hitting the diffuser.

[@Sarah-rf5rj]

The light only passes through certain coordinates, I think you'll still need a diffuser to hit every single nook and cranny.

[@danielb3573]

S. S. If the beam has to travel that much to get to the corner, then there would be no point in mounting the diffuser on the wall because the light would diffuse completely, once it hit the first wall. Which in turn would keep the room completely dark.

[@Silverizael]

The beam of light is at the top of the room, far above the vampires in their coffin (which is why it's hitting the metal walls. You need the diffuser to send that light down to the floor level.

[@treehugger0241]

I don't think you're supposed to be taking these riddles at face value; the stories just set the stage for the brain teasers the videos are _really_ about.

[@thomasr.jackson2940]

Not within the constraints of the puzzle.

[@javierburgre2__147]

A simple yet elegant way. Proceeds to draw the room in a coordinate graph

[@Amanda-rn6tw]

Hi Dan Finkel, your riddles are the best, unsolvable but good.

[@leezhengjie6958]

It's the SE corner. How do I get my answer? Guts, the fastest answer solver.

[@wuvvy6122]

guts can save you forever

[@elizabethp.7354]

I guessed correctly. Whenever there’s an option like for a b or c I always pick the right one but when I have to invent questions to ask alien gods I’m screwed

[@moniquewilliams3560]

omg sameeee

[@iljaradenkovs7150]

The comment is edited, meaning he probably got it wrong and changed it

[@dzula7368]

*it's my first Ted video and i feel blessed with knowledge*

[@MinhVu-yz5rr]

you ain't seen nothing yet bud

[@Selas81]

I will then in turn bess you with knowing that there are many more riddles like this by TED-ED, should be easy to find too.

[@blah7983]

Welcome

[@designz3d]

Welcome aboard.

[@literaIIyshy]

You feel like that with almost every video of theirs

[@games_for_life0_063]

Ted ed: only have minutes till sun comes out Me: drew a grid professionally in pro time Ted ed: 😅

[@SWARTWOODPREP]

Thanks for the fantastic riddle! One of our students, Jon, actually brought it to John, our head instructor. He REALLY liked the Vampire Hunter Riddle and gave his own solution. Here is an alternate solution: kzbin.info/www/bejne/bGrapXZnZ996prs. Hope this helps some people!

[@lauravillarosa5094]

Thank you, this helped a LOT :)

[@katlinhikaru7642]

great way to picture it :)

[@nafisahmad8645]

imaginative and complex riddles like always,keep on going forever ted-ed

[@paulkersey3042]

I imagine getting into the damn building would take forever since every other step you'd have to solve an end game professor layton puzzle.

[@steliostoulis1875]

That's just math.

[@keshawncodysafiyar7208]

No time at all draw a complex drawing Me:what the

[@daerdevvyl4314]

The drawing was for US to understand, not for the vampire hunter. That’s like saying “The zombies are coming for you, Brad Pitt! No time to lose. Let’s get a camera and hire some special effects people.”

[@iaexo]

This is a wonderfully elegant mathematical puzzle, not a riddle. Blew my mind when I first saw a variant of this problem

[@economicapple2609]

Props to the animator for animating the light path.

[@jaybrianrandone5892]

Before I watch the video, the answer is no, I can't solve the riddle

[@marble25]

ted-ed thinks the meaning of riddle is an animated mathematical question.

[@theshuman100]

Riddle me this. Throgmorton has bought 31 watermelons and shares half with his sister. How fast does a sparrow fly?

[@creative_commander4973]

theshuman100 you can’taloupe is the assumed shape of the flight which makes it impossible

[@donavandunn9824]

@@theshuman100 Is it a European or African Sparrow?

[@theshuman100]

@@donavandunn9824 whats the difference? *proceeds to get yeeted

[@LynnHarrod]

Yeah, this bothers me as well. Math word problems are not riddles.

[@ThePurpleKnightmare]

I used my smarts to pass the test because I knew that the diffuser was big enough that the light would hit it long before it ever hit directly on a corner, so any corner will work, but also it's okay to just stay in the room and hold the diffuser. Be your own wall.

[@Gemini-Lion]

I was able to track the rough direction with my finger and actually managed to get it without watching the solution beforehand! :D

[@seth9326]

*_Simon Belmont has entered the chat_*

[@hopechr]

smash bros has entered the chat

[@eggboi4517]

Seth *_Richter Belmont has entered the chat_*

[@HuyenPhan-ir2wo]

Seth *Dracula has left the chat.*

[@George-pp4vr]

Jonathan joestar had joined

[@sanarao8130]

I think that its harder to come up with these riddles than to solve them..😂😂Kudos to the content creators of Ted-Ed

[@Macieks300]

I heard this riddle before. It surely wasn't made by TED-Ed

[@terry_tamali]

Mostly Dan Finkel though.

[@joelwatson9093]

I know nobody will see this comment at this point but I want to present another solution that I think is better because it can be used for any angle or room size. Basically you can visualize how light bounces in a room by flipping the room along the side the light bounces off and having the light travel in a straight line. Now let’s flip the room each time light bounces off the wall but also lets leave a copy of the room where it was before the light bounced off the wall until the light hits a corner (we don’t actually need to know which one yet). Now that we have a straight line of light going from one corner to another we can imagine the light like the diagonal of a rectangle created by extending the sides from each corner the line touches until they meet. More specifically it is a square since the diagonals of squares create 45 degree angles. Now thinking back to how we made our square, we know each side is equal to the length of the original rectangle’s side multiplied by how many times we flipped along that side minus 1 (the minus one is because of the original room), but since it’s a square we must have the length of the sides created by flipping up and sideways be equal. In other words we need the least common multiple of 49 and 78 which just so happens to be them multiplied together. Therefore, to get the light to hit a corner we must flip the room 77 times vertically and 48 times horizontally. Now let’s bring it all together. Think about what happens when you flip the room along a side, if you flip vertically bottom becomes top and if it’s horizontal the left becomes right, but if you flip it again it goes back to normal. If we flip the room a odd number of times the orientation of the room flips along whichever axis we flipped along but if we flip an even number it remains the same. Now the light must hit the top right corner of our rectangle so we can use the parity of how many times we flipped the room to find the orientation of that final room in which the light hits the top right corner. So we flipped up an odd number of times so south is on top and we flipped an even number horizontally meaning east is still on the right, so the top right corner in which the light hits is the south-east corner. This may not be as easy to understand or explain as the solution presented in the video but what I love this solutions versatility. You can use the same principle to find the solution for any problem like this and isn’t dependent on the light coming in at a 5 degree angles dice you can adjust the ratio of the big rectangle’s sides according to the angle. Plus it uses a little bit of real optics which is something we don’t think about very much and I think that this way of thinking about light is really cool. The video’s answer isn’t wrong, I just feel it could just be a little better.

[@Rainy_R]

The vampires in the thumbnail: Is asleep That one vampire on the far left: *i don’t need sleep, I need answers!*

[@whyit487]

*I love seeing the comments under these riddle videos where the commenter points out the fact that in **_real life,_** the **_non-existent mythological creature_** could be defeated another way.*

[@Moist_jellyfish]

Identity theft is not a joke

[@tanviohol6807]

😂

[@suwinkhamchaiwong8382]

Hey, it’s Justin’s cousin.

[@whyit487]

@@suwinkhamchaiwong8382 I just noticed that you replied to one of my comments on "Does someone else have your face?" by It's OK to be Smart, where you said "Preparing the joke?" Well, i guess we both watch the same videos. I'll subscribe to you now.

[@luc8492]

nut

[@Ahlnie]

The "pause the video" section didn't include the dimensions of the room.

[@KJSDASHOPAHOLIC]

I knew my habit of doing diagonals of bathroom tiles would come in handy.

[@commercialchase8442]

It's essestially "Will the DVD logo hit the corner?": The riddle

[@KartheekTammana123]

*Or* you could just put the diffuser at the door, where the light comes in.

[@TheJthedog]

Kartheek Tammana it would be better to just stand in the middle of the room with it in hand

[@jp4431]

Your knowledge of how light works is disturbing

[@user-ld1sn6ur5i]

How will you get out

[@lia5911]

전혜준 after the vampires die

[@fqidz]

Who else is not even trying to answer the riddle?

[@SummerTokyoNeko]

Me... 😂

[@dheepachandhiranm9694]

Definitely me 😂😂

[@carlostheminecraf5523]

Less than normal.

[@SuperSwordman1]

I try, but certain riddles I don't. This is one of them

[@antoniacalderon2257]

Gave up after the first obviously WRONG try... 😒🤣

[@geminigalaxy9623]

Yes because drawing a perfect grid with all the coordinates lined up with perfect precision takes less time then drawing a few lines

[@noir0013]

Why bother if the light bounces of everything anyways. Or it will hit a coffin and that’s that.

[@TheRMeerkerk]

Create a grid of mirrored rooms and draw the 45 degree line through those rooms until it hits a corner. This will happen when a corner has coordinates (x,x). Since all room corners are at coordinates (78n,49m), we just have to solve 78n = 49m. We know that 78 = 2 x 3 x 13 and 49 = 7 x 7, so the first corner that gets hit by the line is at coordinates (2 x 3 x 13 x 7 x 7, 2 x 3 x 13 x 7 x 7), which means n = 49 and m = 78. So after 49 horizontal mirrors and 78 vertical mirrors we hit a corner. If both were 1, then we'd hit the NE corner, if n = 2, then we'd hit NW, for n = 3 NE again, so if n is odd and m = 1, then we hit the NE corner. If m = 2 and n is odd, then we'd hit the SE corner, and if m became odd again, we'd hit NE again. So for even m and odd n the light will hit the SE corner. Answer: SE corner.

[@TheRMeerkerk]

wow for once my method to get to the answer is slightly different

[@zmaj12321]

Ooh this is how I did it.

[@Macieks300]

I did it the same way: my explanation: kzbin.info/www/bejne/hmWQn2N_graGqLM&lc=UgxKN_EoqbgFy_lcf6B4AaABAg

[@Epaminaidos]

Yep, that's how I did it as well.

[@MrKenkron]

Same. This works for all cases too. (I think the video's method does as well if you divide the walls by the greatest common factor first).

[@KnakuanaRka]

I thought about this one in an entirely different way: basically, since the light travels at 45 degrees, the total distance it moves north-south has to be the same as the total traveled east-west. In order for it to hit a corner, this distance has to be a multiple of both dimensions of the room. Since 49’s only factor is 7, and 78 is obviously 1 off from a multiple of that, the lowest common multiple of them has to be their product. Therefore, as the light bounces around until it hits the corner, it must travel 49*78 meters in both the up-down dimension and the left-right one, so it travels the north-south range of the room 78 times, which is even, so it ends at the same side it started (south), and the east-west range 49 times, which is odd, making it end on the opposite side from where it started (east). Therefore, the diffuser must be mounted on the southeast corner. Also, once again, who comes up with these titles? Why not call this the Reflecting Light riddle?

[@dryzalizer]

Well done, even simpler than the given explanation.

[@KnakuanaRka]

dryzalizer Sure; I especially favor it because it actually demonstrates that it will go through that point. Sure, you can mark all the points with even coordinate sum and say that it’s possible for it to go through those points, but does that prove it will? The way I handled it actually shows that. Also, my version can handle cases where both dimensions are even. Imagine trying the video’s solution on a room with dimensions like 16*20; all four corners would be open, and you would be stuck. My solution automatically removes the common factor of 4, reducing the dimensions to the equivalent 4 and 5 and getting a solution.

[@huaen8880]

I have a similar explanation to yours! Mine relies on estimating 49 and 78 to 50 and 80 to simplify things, but it's close enough.

[@tomheyworth6020]

Yes, I did it the same way. It's really a modular arithmetic problem.

[@TheMoped]

I didn't know i can move is a north-south direction

[@SpurritialTheories]

Even better solution 1.Invite all vampires to a party at night 2.Wait till everyone's there 3.Activate a disco ball

[@DarkSciencez]

The light would hit a corner when it reaches the lowest common multiple of 49 and 78. Since those numbers have no cofactors, the light beam would travel 49 * 78 = 3822 meters before hitting a corner. The light hits a south corner if the distance it is a multiple of 49*2 = 98 and a north corner otherwise. The light hits a west corner if the distance is a multiple of 78*2 = 156 and an east corner otherwise. Therefore the light would hit the southeast corner, and you can use similair logic for other room dimensions.

[@BigMastah79]

“The sun will be in position soon” “Let’s draw a graph”

[@brendanmurphy4034]

Oh my god....It’s the bouncing DVD riddle.

[@janicedsilva16]

1:35 wait if it’s gonna be morning wouldn’t they be asleep by then......? They’ll be locked in their caskets/ coffins, right?

[@buhbo3250]

I instantly guessed the SE corner, but that's because any time ive ever seen a dvd screensaver hit the corner it was the se corner

[@matiasherrneder4254]

I had a simpler solution (sorry for my english): The light travels at a 45° angle, so both X and Y coordinates add equaly. This means that if the first wall is, for example, 43m long and the other one 22m, in a given time the light will travel 22 times the first wall and 43 times the smaller one, at this point, it finds a corner. This will also happen with any other common multiplier (idk if it's called that) of the two numbers. Anyway, if the light travels a wall an even number of times it means it will finish on the same point for that wall, if it's an uneven nuber of times, it will finish on the opposite end. Now take this example and solve the video's riddle with it :).

[@MrAaron317]

thank you, i thought i'd be the only one with this solution

[@MrSlothJunior]

I would not call that a "simpler" solution.

[@austindelacruz5872]

But then you wouldn't which exact corner the light would hit as there are two wall with those measurements

[@matiasherrneder4254]

@@austindelacruz5872 well, you have two axis that can be either even or uneven, you cover the four possibilities.

[@galladegamer3579]

You hear that? That's the sound of my brain melting.

[@NewbyTon]

Just hire a werewolf

[@NewbyTon]

It's all a connected plot

[@PerceptionVsReality333]

There are vampires that can easily defeat werewolves.

[@TheMoped]

Sorry but they take __***Months***__ to find and hiring them, we are in a __***DIRE***__ situation

[@cisforcringe5645]

Newby Ton Bruh how would you even CONTROL a werewolf?

[@wobblyorbee279]

are we just ignore how well the question is made? like WOW....... it seems complicated but when you see the solution its suprisingly surprising.... like I CANT EXPLAIN.. like the top two corners are even and odd numbers, and the one that is both the same parity are the bottom ones... LIKE HOW DID THEY THINK ABOUT THIS QUESTION?! where did they start? this is incredibly incredible. i know i may be overreacting but this question is just.... wonderful, well made, original

[@Mystixor]

Another interesting way of solving this: Instead of reflecting the beam off a wall, imagine mirroring the room on the wall the beam hit. This way, you can view the beam as still moving in the same direction as before, but in a mirrored room. Because of the 45°, the beam shot from coordinates 0, 0 will always be on coordinates that are equal in x and y and eventually hit the upper right corner of a mirrored room. It will hit the corner of a mirrored room at the smallest multiple of 49m and 78 (which is 49*78), meaning 49 rooms in the horizontal direction and 78 rooms in the other. If you now simply realize the odd number of rooms has the last mirrored room mirrored back to its original direction in that dimension, and an even number does the opposite, it becomes clear the room is not mirrored in the horizontal direction (the corner the beam will hit is on the right side) but mirrored in the vertical direction (the corner the beam will hit is on the bottom) you have solved the puzzle. I know in text this seems like a huge thing but once you follow along and visualize it in your head it should become quite clear 😊

[@crazymanmot]

The list of hints didn't include the dimensions of the room tho.

[@thislopop2700]

1:08

[@boiledham]

@@thislopop2700 1:35

[@adityagiri3600]

3:12 why do you wanna put that globy thing if there's already so much light reflected by the walls?

[@bigbakerboi3872]

That light would be a beam, which would only strike the walls above the coffins, not the entire room. The diffuser will spread light in all directions.

[@bigbakerboi3872]

@@adityagiri3600 So? You asked a question and I provided an answer. I don't care if you're anyone. And why does my age matter?

[@monochromeart7311]

@@adityagiri3600 hi doc, if you're such a "genius" why couldn't you understand simple logic from the riddle???

[@TheMoped]

@@adityagiri3600 if you are actually a professor from a non-existent university, you should care about grammar or not use when you don't feel like it, why you capitalize the U instead of both or none. You seemed to care when you started your first two sentences and added question marks. My only theory is that you used Grammarly and it didn't recognize the fake university name and didn't bother to check it.

[@adityagiri3600]

@@monochromeart7311 who says I didn't? I am a huge fan of Ted Ed riddles!

[@preach9]

The only riddle I finally got right, by just guessing of course.

[@thecoolcongle5128]

0:56 that's not how physics work

[@kerithwooldridge]

How would you get/know the dimensions of the room if it's a secret lair?

[@TheExoplanetsChannel]

Love these riddles!

[@NikoCubeRoot]

Dracula S

[@owenlewis4693]

They're not riddles. They're math problems.

[@ais8195]

first timer to understand the answer, amazing

[@rivermike18]

This is the first out of four Riddle videos that I’ve watched where I was correct