Check your intuition: The birthday problem - David Knuffke 

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

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

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

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 😂

Sanjivanie dude 😂😂

Sanjivanie lol😂😂

Therefore you aren't.

Same

Lmao nice one 😂

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

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 😭😭🤦🏻‍♀️

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!

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 😳

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!!

Ego is quite a strange tool

Me too. At 29, but in the workplace.

Sounds like the beginning of the Disney Ckassic "The Parent Trap". Lol

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.

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.

If you're wondering, the probability is 5.6%

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

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?

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...)

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?

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 🤣

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

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.

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.

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?

Shawn Ravenfire f

Shawn Ravenfire ,

lmao totally

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

TaylorDaMidget Yep, I was thinking the same thing

thank you

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

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.

cooldude56g i think they are bullshitting in this video

That's how probabilities work. There is a 99.9999% chance of life not existing in the universe, yet life exists anyway. Just because something is likely doesn't mean it MUST happen and vice versa.

cooldude56g well obviously the maths is wrong and you are right...

+wormald its let's exploding ur mind but ur correct

That's probably why probabilities aren't absolute predictions. ¯\_(ツ)_/¯

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” 😆 😂

wait, that's illegal.

My friend was born October 9, 2008.

Not neccessarily, 366 people can all have separate birthdays, that's not including people who have not been born yet, and those who had to be removed prematurely via C section, and thus is debatable whether or not they were truly ever born. Ergo there are groups of millions who do not share a birthday.

Yes, it's obvious that if a group has 365 people, at least 1 pair shares the same birthday. Does it answer the question asked in the video? No. Your comment and the topic of the video are completely different

Caston Young Then how _can_ they not share a birthday?

T 42 Actually, each person could have individual birthdays if they had exactly one birthday per day.

Leap years

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

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 🎉🎉🎉🎉🎉🎉🎉🎉

Shivraj Rathod here

🙋

.

pi day to be exact

Me too

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

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?