
Probability and Statistics Basic Probability and Statistics Math Forum 
 LinkBack  Thread Tools  Display Modes 
December 5th, 2016, 11:28 AM  #1  
Newbie Joined: Dec 2016 From: kljlçjkçlkjç Posts: 2 Thanks: 0  Probability to be born on a specific day
Problem: Quote:
I don't understand the two formulas (for getting 7.9% and for 70%). Could someone explain me, please?  
December 5th, 2016, 02:12 PM  #2 
Global Moderator Joined: May 2007 Posts: 6,205 Thanks: 487 
Prob. not a specified date (Sep. 16) for one person is 364/365. Birthdays are assumed independent, so prob. that n people's birthday is not on specified date is $\displaystyle (\frac{364}{365})^n$, based on general rule that the probability of n independent events all happening is the product of the individual probabilities. For the second question: The probability that two people have different birthdays is 364/365. For 3 people it is (364/365)(363/365). etc. 
December 6th, 2016, 02:47 AM  #3 
Newbie Joined: Dec 2016 From: kljlçjkçlkjç Posts: 2 Thanks: 0 
ty very much mathman. the wikipedia link has a reference explaining the formula that I had not seen: http://mathforum.org/dr.math/faq/faq.birthdayprob.html 

Tags 
born, day, probability, specific 
Thread Tools  
Display Modes  

Similar Threads  
Thread  Thread Starter  Forum  Replies  Last Post 
a specific angle  William Labbett  Trigonometry  2  January 4th, 2015 02:18 PM 
specific search  andreaugust  Number Theory  2  July 15th, 2013 05:30 AM 
calculating probability for getting specific cards  azarat  Algebra  4  December 9th, 2009 06:39 PM 
The Probability of a Specific Indeterminate..?  James S Saint  Advanced Statistics  12  November 4th, 2009 01:12 PM 
probability of getting a specific cardgroup with 9 people  durexlw  Algebra  0  April 5th, 2009 04:54 AM 