Birthday Probability Problem

The probability that at least 2 people in a room of 30 share the same birthday.

Category:

Education

Tags:

• probability
• birthday

[paulceltics]

100th like is me

[higgx]

Well, this assume that the birthdays are evenly spread throughout the year, which I guess is not the case.

[Nixarzius]

This is the Birthday paradox, you can read about it on Wikipedia as well.

[DemonikOu]

Surprising conclusion! 70,63%, wow!! I guess it's even higher if we take into consideration that more people are born on specific months..

[jamesahibbard]

The assumptions/simplifications not stated in this video, and I don't like people that don't state they are making assumptions/simplifications like this, but otherwise its an awesome video, are

A. We are ignoring leap years, they do complicate things

B. We are assuming a even distribution of birthdays throughout the year, (which doesn't happen)

[jamesahibbard]

@abennett4 it occours in 97 of 400 years actually. Our calander operates on a 400 year cycle (including days of the week (ie it will be a Thursday on January 19th 2412, because today, January 12th 2012 its a Thursday)

However it is also far more complicated than you have tried to simplify it there.

[angryparrot1]

my TI-84 keeps exploding

[legoman8901]

Thanks im finished with my hw

[maximveksler]

@renduke That's not the same question and definitely not the same probability. To use your analogy you should write on 30 notes random numbers between 1 to 365, now after your finished writing the numbers go check if the same number appears on at least 2 notes. 70% of the times you will find such number. Regrading the hat - Well you can use it to take if off for Sal which is probably the best teacher in the world :)

[abennett4]

@Nickondeweb No Yrda1 is right. The probability is 100%. It is not the probability that someone would share your birthday. It is the probability that some combination of TWO people would share the same birthday. Two entirely different questions. The assumption in this video (and implicit in Yrda1's comment) is that there is no leap year.

[abennett4]

@iphoneluvr Actually, if you were to include leap year, you would have to assume there were 365.24 birthdays (february 29 only occurs about 24 out of 100 years). Anyway, includeing leap year would only chage the answer ever so slightly. Wer're talking ~.01&.