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- เผยแพร่เมื่อ 3 พ.ค. 2017
- View full lesson: ed.ted.com/lessons/check-your-...
Imagine a group of people. How big do you think the group would have to be before there’s more than a 50% chance that two people in the group have the same birthday? The answer is … probably lower than you think. David Knuffke explains how the birthday problem exposes our often-poor intuition when it comes to probability.
Lesson by David Knuffke, animation by TED-Ed.
i dont even wanna know how difficult the editing of this video was
Don't worry, I'm sure the lines to each weren't added in manually
i was thinking the same in stead of the math
Shut up! You're Hermione. 😁 You must be good in Maths 👍
Hello Hermione
pxrenatxre
Hi
When you figured you just watched a full math lesson willingly
I am just reading comments over here.... Not watching the video... 😂😂😂😂
I wanted to test my intuition but I realized I had solved this exact problem a few days ago😭😆
Lmao true
I wish Math in school was this interesting 😅
Nah I just dipped at 1:45 😂
"take a moment to think about it"
Me: bold of you to assume I think
Sanjivanie dude 😂😂
Sanjivanie lol😂😂
Therefore you aren't.
Same
Lmao nice one 😂
I had three people in my class who all had the same birthday. Same month, same year, same day. Funny thing was, they’re all best friends
Wow ,they wouldn't call anyone to their party then.
Me and my best friend have same birthday too. Not same year tho.
And that’s on zodiac signs
My best friend and I had the same birthday, we even have the same first name. She is one hour older than me.
Same year in a school class is not so uncommon because you are already divided by age
"ignore leap years"
me a person born in February 29th: ok then
When do you celebrate your birthday in normal years?
@@ruchalondhe9032 march 1th but depends
@@virginialira9477 *1st
@@greyslaurenciana9249 👍
Same born 29 Feb and kind of funny when people ask me how old I am...two or three
Funny thing is in my 10 years of school with an average of 25 students in the class, nobody had shared birthdays
Lelouch Yagami did you ask for everyone's birthday? did you consider the birthday's over the weekend, holidays, and breaks?
Lelouch Yagami Because the year that you and your classmates are born on are the same so the chances decrease
No, the fact that they were born on the same year has no effect on the probability two people had the same birthday.
Well in my class of 38 none share a birthday but I have a fren that's birthday is one day before me
Yeah same! I have only met one person in my life that shares the same birthday as me! Even as I did extra-school classes
i didn’t understand like any of that but yum cupcakes
Lmao
😂😂
It's all about having the same bday in a group.
Lnaoo same
Literally me. Not only did I not understand the video, but now I'm craving cupcakes 😭😭🤦🏻♀️
My initial guess was about 24. As a classroom teacher, I notice it is common for a shared birthday to occur about every other year or so. Having just looked at my roster today, and specifically the birthdays, I did notice a shared birthday this year. So I based my guess on experience rather than statistics!
Ahh I see. I guess teachers have seen the amount of shared birthdays per class/grade. As a student I guessed around 100 people. My graduating class has around 300 kids and i share a birthday with 3 of them. Crazy rightt
My guess was infinity
wow thats so cool
interesting!
I just think the other factor why our basic intuition can't grasp the math is because our brain have small room to imagine the pairs. I mean, when this question come up, people tend to imagine about to pair their own birthday with just small group people, abandoning that each of one in 23 is pairing with others. So, this makes first dial signal into our brain that "it is hard to find match YOUR birthday with only 22 people". Then we end up realize that "Oh yeah this question supposed to pairs each people, not only one"
Muhammad Fadlullah hey, nice thought!
which means that humans are kinda selfish, they only think of their own perspective of things and ignore others
@@AladynG yes but, evolutionary, this makes perfect sense. we wouldn't have been able to survive if we "wasted time and resources" thinking about others instead of putting ourselves into the centre of our thoughts
@@insertnames well played
True!!
Sorry for the double upload! We had to fix a quick error and wanted to get you all the corrected video right away. Here it is -- please enjoy and thanks for watching!
TED-Ed yay!
Now i want to know what the error was.
TED-Ed can i get a answer to my answer? Sometimes we hit special point on elbow on anything and it pains tooo badly and feels like being shocked. Please could you explain it
Inder Saini it's because in that spot there is a nerve that is really exposed, and unlike other nerves protected by bones or other things this one is really easy to touch and hit accidentaly. The pain is horrible because muscles are very weak to that stuff.
ΠІΠЈΛ uh thnks bro 😳
The probability of a match
A MATCH
So many good jokes
In my first psychology class in college, the professor used this as a way to show that people’s intuition and "common sense" is often wrong. While it’s really a mathematical puzzle, the fact that most people are wrong about this gives us insight into psychology.
The class had about 150 students in it. The professor had each of us guess how many people he’d have to call on to find two who had the same birthday. We all wrote down our answers, then he had us sit in sections of the lecture hall based on the number we’d chosen. Most people selected a number greater than 150, reasoning that you’d have to go through birthdates for half the year before you were likely to find a match.
He then started asking each student what their birthdate was. He’d write the date on the chalkboard. We reached the first match at like the 12th person he called on. He said that we’d throw that result out since it was just coincidental that we’d found a match so quickly. He kept going. The next match happened on about person number 21. He kept going, wanting to show us where we’d reach a point where almost every new birthdate was a match. We got there by person number 60-something. By the time we were into the 70s, pretty much every new birthdate matched someone else’s.
He explained the mathematics behind it, yet there were still people in the class that said it was impossible to have so many matches in a group that small. He asked them to explain why it worked, though, since we’d all seen it with our own eyes. They said it just defied common sense. The professor said that this is why "book smarts" almost always trumps "common sense." Most people simply can’t comprehend that.
Ego is quite a strange tool
My intuition: Ok let's try to find out what the answer could... urgh it involves math calculation sorry i can't do nothing for you
You can't do nothing? That's a double negation, which means that you can solve it. I'll be waiting for your solution.
aThrasheR shhhhhhut up
aThrasheR
Even though that's a double negation, it's sort of a slang (maybe) some people use to make a single negation.
There might be an explanation somewhere, but I'm too lazy to search for it.
It's not slang, it's just grammar. Most languages outside of the Germanic language family actually REQUIRE the use of double negation (French, Spanish, Portuguese, etc.). There are also dialects of English that use double negatives (AAVE being one of them).
It's a huge myth that double negatives make a positive, when talking about language.
I speak French and I can tell you that the "double negation" you're talking about that is required isn't actually one. It's just one negation that requires two words and that's totally different. An actual double negative in French makes a positive.
I wonder how after all of my years at school, I’ve never met a person with the same birthday!
Same
Nopes.. Infact i had shared my birthday once with my classmate 😅😅 who was just my partner 😵...
What a boomer it was for me!
@@abbreviatedalex2418 This is so true. I used to think that it would be impossible to find someone who shares my birthday, or at least that I haven't met anyone who shares my birthday, but then I ran into a friend in London (We're both chinese) and then to our surprise we realised that we had the same birthday.
(and then I forgot about it because the idea that someone shared my birthday was still foreign to me, so I forgot to wish her happy birthday on my birthday 😢）
because it's any two people not you and someone else
I share my birthday with my own brother who's 8years elder than me.
I have a friend who was born on the same yr, same day, in the same city, in the same hospital as me! We were born just hrs apart from each other. We just so happened to meet at a summer camp on Atlanta when we were 22!
Me too. At 29, but in the workplace.
Sounds like the beginning of the Disney Ckassic "The Parent Trap". Lol
this made statistics sound a lot more interesting suddenly I remember doing combinations
What a coincidence! You uploaded this on my birthday 😂🎂✨
simplymaci may the 4th be with you
It was my birthday too!
It's my sister's birthday on May 4th too.
With such massive number of viewers its not a big deal. There are thousands like you.
simplymaci , as well as in the birthday of another 2000~ viewers of this video
I just have to say, that the editing of the video is amazing and pretty entertaining, I love it!
I have watched so many ted ed videos that Addison Anderson's voice comes to me in my dreams.
When I was in school, my school van had a total of 7 people and 3 out of them shared the same bday (Me, my younger brother and the van owner’s son) Surprisingly enough, 3 people in the van also shared the same name (my brother, the van owner’s son and another girl)
Even more surprising is that both my brother and the van owner’s son are left handed and were the piano prodigies of the school😭😭
It feels so weird till this day
I don't understand any of this but I still love it
Wtf??? How???
Me toooooo
Want an explanation?
@@bengal_tiger1984 sure I have difficulty understanding too
There are 365 days in a typical year. Our scenario works without accounting for leap years, twins etcetera.
So we have 23 people in a room right? Our current aim is to calculate the probability of 23 people NOT sharing a birthday.
Let's start off with the chances that two people have the same birthday. The first person who we will call Allie can have a birthday any day of the year. So now we account for that particular birthday, we assume that the next person Blair can only have their birthday in all of the remaining days of the year (her birthday is not the same as Allie's.)
You know how when you roll a single die, you ask yourself what is the chance that you will have a five followed by a four? Without considering the many variables in our world and only concentrating on pure probability, we multiply the 1/6 by 1/6. It doesn't really matter whether what the following number is four or whatever; it is independent of repetition since it is a single die. The probability of getting this combination is 1/36 now. Same with unbiased coins, probability of getting two heads in a row is the same as a head followed by a tail.
This connects to the birthday problem as the probabilities are all multiplied. For Allie and Blair, we would say 365/365 * 364/365 which gives us roughly 0.9972 so the percentage is 99.72%. That is the probability that Blair and Allie DO NOT share the same birthday.
Now let us return to the scenario with 23 people in the room. We do the same as we did for Blair and Allie, but just as we reduced the numerator by 1 for Blair, we keep repeating. 365/365 * 364/365 * 363/365... Until we reach 365 - 23 (for the people in the room) which is roughly 342. Then we multiply all of these. After that, we divide that answer by 365 to the power of 23 as you can see that 365 has been multiplied by itself 23 times. We didn't have to do this to Allie and Blair previously as Allie's 365/365 cancelled out and made 1. But that is how we attain the probability of none of the 23 people sharing the same birthday. That is roughly 0.4927 or 49.27%. Now by deducting by 1 or 100, we get 0.5073 or 50.73%. That is the probability that at least two people in this group of 23 share the same birthday!
To make this easier, we can use the formula n!/(n - k)! /n ^ k. n represents the number of days in the year here, which is 365. k is the number of people in the group here, which is 23. As explained, 365 is multiplied 23 times so it is divided by 365 to the power of 23. The factorials make it easier rather than the tedious reduction process (it'd be a pain to repeat those fractions 23 times!) as they are after all multiplied by each other in order such as 1 * 2 * 3 could just be written as 3!. Yes, you noticed how different the formula looks from the method we used with the factorial of n on the numerator and the n - k in the denominator but it reflects that process of ours basically.
Hope this explanation helped you understand... Feel free to ask any more questions and point out any errors! Now try one of your own, what is the probability that out of a group of 10 friends, at least two share the same classes in a school with 50 different class options? (Made this one on the fly...)
I'm always a sucker for collage and animation
*In college I shared a room with SIX of my friends and TWO of them had the same birthday.*
I was wondering the odds and thought it's almost impossible but thank to you I can understand it better now.
If you're wondering, the probability is 5.6%
I’ve never been a fan of math, but this video explains combination quite well! Really easy to understand 👌
We looked at this in my data management class! Loved the video because as someone who dislikes math more than anything in the world, this video was really well done and gave a great insightful explanation!
i watched this because yesterday was my birthday. turns out there was another girl with the same birthday as me in my class of 23 people. legit blew my mind
Gosh infact me too sharing my birthday with my classmate 😵 who just sits next to me. Can you imagine that.... It was like boom.. 99.9% chance out off 24 students 🤣
if only i find this video earlier, must have been really helpful for my math exam. idk why but this video explanation is quite easier to understand about the concept.
I absolutely love these editing skillz.
i love how this was uploaded on my birthday
I've asked a few people in my life about this question. I believe the reason they don't come close is not one of intuition, but misunderstanding the question. They seem to "fix" a date in their minds, i.e. their birthday, and ask a different question, "How many would it take to have my birthday?" Great question!
Reads the title: Haha jokes on u I’m a twin
Two seconds in: nm
0:50 "why is our intuition so wrong" me who guessed 25 when the answer is 23... 👁👄👁
Same
I guessed 26😁
I don’t get the point of this comment/replies. You got it wrong so you’re saying “lol intuition is so wrong cause I was wrong” but also you’re telling us your guess which is close but out by a few so are we supposed to be impressed by this!? I’m so confused hahaha what is your INTENT, PEOPLE
@@eilzmo i was mocking the quote from the video by pointing out my own answer which was close, basically sarcasm cause intuition can actually be correct
To anyone reading this comment, its not my birthday.
Have a like.
A very merry unbirthday to you! (Yes, you.)
It is not my birthday either. What a coincidence?!
happy existingday
David S. wouldn't 'unbirthday' in theory, be death?
*BEEP*
*BEEP*
[Incoming "today is my birthday" comments alert]
4 7/7 There is a kid in my school that had a birthday today xD
*Meow Meow* I'm a Cow, I said *Meow Meow* I'm a-NOO!!!!
Look up 'Beep Beep I'm a Sheep' And 'Meow Meow I'm a Cow'
Super7ups VlogsAndVids ASDF!!!! you understand me!
u were born on star wars day?
This is the first time in my life that I clicked on a TED-Ed video and already knew about the content and how to calculate this and I am so proud of myself atm xD
*"why was our Intuition so wrong"*
No honey, it aint , Im bad at math!
I love the visuals on this episode so much! And happy birthday to everyone, everyday, bc my intuition tells me that at least one who reads the comments has birthday
It's my birthday! I'm 24 now! Happy birthday to me!
Maithun happy birthday !
Как вам мои рисунки?)
Maithun fuck you
it's my birthday too! I'm 24 now as well! :D
go fuck yourself. Also, happy birthday.
I enjoyed this video. I had a basic understanding of the birthday paradox before this, but this helped me understand so much more!
Woahhhhh, math is just so cool!!!
Especially the combinatorics part of it, where you actually dont need any prerequisites to understand it.
Indeed amazing!
3:32
That moment when TED-Ed starts to summon Satan with math
My math teacher proposed this same question to us, and I said that is was very unlikely. I was very shocked when another girl in my class had the same birthday as me.
No one gonna talk about how their heads were all put on a stake?
My college roommates and I all had the same birthday, born the same year and all three of us was hours apart.
Edit: Also I have a best friend, she and her brother are born on the same day but a year apart. Lol
Again wow...3 the same year, roommates, and within hours...when you consider that people vary more in ages, in college, it seems as if the probability of the same year would decrease... but I'm no statistician.
Woah🤐
Are you still friends with your roommates though?
Or to put it more simply, we're quick to assume how unlikely it is that someone else in such a small group would have OUR OWN same birthday, but we forget to account for someone else having the same birthday as a DIFFERENT someone else. It's less to do with non-linear functions and more to do with egocentricism.
Shawn Ravenfire f
Shawn Ravenfire ,
lmao totally
This animation is impressive! Well done.
This editing is nuts. So much work...
I love the collage-esque animation in this one quite a lot :) Great vid!!
The "everything happens for a reason" people need to watch this video.
GuildOfCalamity 😂
I don't think the 'everything happens for a reason' people have anything to do with this. They do not have that motto because they believe (or not) in coincidences and stuff. It's about how every situation can be beneficial.
GuildOfCalamity actually, I believe both in fate and logic. However, life itself is magical, why take all that magic away? After all, not everything can be perfectly explained. I believe in fate yet my intuition with this question was spot on, that was before I did the long math.
Edited to make my point clearer.
GuildOfCalamity GuildOfCalamity and I also agree with Katerina, many of "the 'everything happens for a reason' people" don't necessarily equate this belief to fate but that every situation, fate or otherwise is beneficial or needed in some way. Your inability to open your mind to the thinking of others will be your downfall.
But everything indeed does happen for a reason. It's cause and effect. Every occurrence has been caused by all the necessary factors to make it possible, and this occurrence in turn will become one of the factors for any other occurrences that will follow up.
Hey everyone it's actually my birthday today I found this in my feed and started laughing really hard😋
I watch this video from time to time, but my brain still doubts it at first and then becomes amazed again by the end of the video.
such a well made ,well explained and extraordinarily edited video
TED-Ed : Try calculating the possibilities of people in your group having the same birthday as you.
Me : I can just ask my friends you know
TED-Ed : I-
wait, that's illegal.
love this vid
Didn’t understand a word you said but I agree. You have a genius mind.
This problem inspired me to make a whole Java program that makes runs these simulations so I don’t have to guess or even do much math really. Using just the law of large numbers and a lot of computing power, I can let the computer do all the work.
This was recommended on my birthday
This is a common question we get in IIT-JEE
That's exactly what I thought during the video
U mean jee mains and advanced
I'm like twelve but whats IIT-JEE
@@leonkirk8327 ,it is the most difficult engineering entrance exam in India
This video tripped me oooooout!!!!!! LOL because I did NOT learn this in high school and I am in college.This is mind blowing!
Great video wow its like sharing the same amount of anything, between a small anount of people changes of us getting the same are large
wait they really re uploaded this just to change the less than symbols to more than symbols
TaylorDaMidget Yep, I was thinking the same thing
thank you
I just crack an egg on my forehead rather than on pan after watching this...
Help Me...😨😨😨
silly, now you have egg on your face
King Armish I read that as “I just crack my forehead on a pan rather than an egg” 😆 😂
I had that situation from begining. In my class was 23 people in primary school and one person has birthday this same day like me and even more: his mother was in this same room in hospital with my mum when they was at the finish of pregnancy.
all my combination nightmares from high school are gonna come back tonight, thank you!
I remember my classmate who were beside me when we were in an immersion. He just randomly blurted out that his birthday is Dec6, same as mine. 😂
Today is my birthday and nobody celebrated it with me. No family or friends. Then I ended up looking at birthday videos just to spite myself. Hahaha
I'll wish you then
"Happy Birthday Dear"
"May you have many more"
Eat lots of sweets🍭🍬🍭🍬
@@fz1792 Thank youu! I did eat sweets a year ago. Another birthday of mine has passed and this time it was different. It just shows that you must held on so you're there for a changed future. 💜
Happy belated birthday
Happiest birthday to u 🎉🎉🎉🎉🎉🎉🎉🎉
Definitely Ted Ed videos are more interesting than school.......❤️
I have the same birthday, same day and month as a famous musician in my country, I intially thought that it was a coincidence and was quite shocked about it, while my friends were so surprised that when I answered my birthday, they immediately talked to each other. I didn’t know what they were talking about
And it still took me 20 years to bump into someone. Sometimes coincidences ARE as coincidental as they seem :P
Who be that?
You of course lol :P
Is it in February?
Kyla Renee Yes. February + 7 :P
Kunjika Prasai Fun Fact : The least popular birth month is January-February.
The question was "how big a group has to be", so I expected we'll find that size from scratch. But the video "picks" 23 as the size already and then explains how!
Solving for the number is a little bit tedious and not that interesting. I feel like the point of the video is to show that it's counterintuitive, not to work through an equation
I build a sheet in Excel to randomly generate 23 numbers between 1 and 365, with an alert whenever there was a match. I ran it 70 times and got an even 35:35 match/no match. Wild!!
Me and my boyfriend share the same birthday and year, 2 hours apart, and born in different countries. I came to his town as a foreign student. We met in a restaurant where I worked and happily in love since.
In my 5th grade class there were not 1, not 2, but 3 people with the exact same birthday!! (November 7th)
That's amazing because that's so rare! In a class of 30 students, the probability that exactly three of them share a birthday is 1.05%. In a class of 50 students, the probability drops to a mere 0.58%. In a class of 60 students, it drops even further to 0.21%. In a class of 100, the value is just 0.00007%.
@@ultraviolet.catastrophe shouldnt the probability get higher with more people getting involved? :D
@@mikescholer1995 That's a very good question. The answer is no. It's a counter-intuitive problem, that's why it seems the probability should get higher when more people are involved. In reality, the probability decreases because we are dealing with "exactly three people" and not "three people or more". Think of a football stadium. Or is it soccer? Whatever. The stadium has 100,000 people in attendance. What is the probability that JUST THREE PEOPLE have January 1st as their birthday? Which is to say, NONE of the other 99,997 people have Jan 1st as their birthday? Basically 0%. Allow me to be daring and claim, "that can never happen." I hope I have clarified things for you. Remember, we are interested in a scenario of EXACTLY THREE people and not THREE OR MORE.
@@ultraviolet.catastrophe Ah i was thinking about 3 or more thats why i was irritated :D
Thanks for clearing that up!
There was 4 people (including me and my best friend) with the same birthday out of around 200 people. July 27th. My brothers birthday is July 28th so he was almost the fifth
posted on my birthday! cool!
no, it's actually my brother's birthday tomorrow 😂😂😂
what are the odds :P
Eyy-Its-Me XD May The 4th Be With You
I guess there was a 364/365 chance of that happening lol
Eyy-Its-Me XD i guessed the question very close to the answer which is 24.. because 2 people have the same birthday in my class.. theres 24 people in my class
I remember reading about this in Adam Fawer's book Improbable and I couldn't understand the problem back then as well.
thank you you just made be interested in a math problem and that's huge
Ya’ll not gonna believe me, but I legit thought “Like... 20 people?” When he asked the question at the beginning. So I’m not even one minute in and I already won. I am the stats king.
funny how during a school exchange i was matched with a person born on the exact same day as me :)
My best friend of 30 yrs was only two days older then me, always felt that our almost shared birthday was a contributing factor to how long the friendship lasted.
I used to have 2 classmates with the same birthday, and once when we were in a split class, a girl in the other grade had my same birthday. What was ironic was that I was like her, and her best friend was like my best friend! We both also had a friend who'd rather play sports than just hang out and talk. We all became great friends!
imagine having 2 friends on the same birthday how will you go to both of their birthdays. ;c
and yes my friends have the same bday.
I said 25 and it’s 23. I didn’t calculate at all. I just guessed. Isn’t intuition about feeling and instinct anyways? Why is this about math?
Great video editing and also math well explained.
just saw this on my birthday. coincidence that I really appreciated :))
TH-cam's recommendation wants to remind me that it is my birthday today.
In my class of 25 people, we have 2 pairs with the same birthday... Huh
In my math class last year there I sat in front of this girl the entire year and it wasn’t until the last week of school we found out we had the same birthday, it was so cool since I’ve never met anyone with my birthday before
This is an amazingly genius animation
I share the same birthday with my brother. He’s three years older than me-
Why did I just sit here and watch this
The animation is out of the world.
Never shared a birthday in elementary and high school. But i did with my english lit class back in college!! We're roughly 20 haha :) learned this in math class so i am already familiar but this video is very comprehensible!! Kudos ♡
Everyone: Talking about the math
Me: Getting creeped by the smiling heads on the sticks
I guessed 20 people before you even said "the number is suprisingly low" am i genius
same! and was looking for this
I can believe this. I know couple of people who has same birthday as me, such as my 7th - 9th grade school English teacher, my fellow student at college (we have exactly same birthday, and our class had about 70 students), the children of my really close friend (we have been friends since our childhood) and the children of coworker.
I love the animation and sounds
There are 3 other kids in my class with the same birthday as me, so when we all have birthday parties no-one goes to mine :(((
Turbo lol, my birthday is when holiday start so no one celebrate my birthday(even say happy birthday) because they go to other place and,have fun with their family. When is your birthday?
**waits patiently for that comment that says, “This video was uploaded on my birthday!”**
I'd heard the stat a long time ago but this video actually helped it fully make sense. The focus shouldn't be on "wow, same birthdays" but rather, more people=more possible pairs=less "wow, same birthdays." So a group of 5 strangers having 2 with same bday? WOW. A pair in 100 people, duh/boring. In 1000 people, probably quite a few pairs of birthday twinsies.
The editing was incredible