SOLUTION: How many people would you need in a group to ensure a 99.9% probability of two of them sharing the same birthday?

Algebra ->  Probability-and-statistics -> SOLUTION: How many people would you need in a group to ensure a 99.9% probability of two of them sharing the same birthday?       Log On


   

Question 1172639: How many people would you need in a group to ensure a 99.9% probability of two of them sharing the same birthday?


Found 2 solutions by ewatrrr, ikleyn:
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!


Hi  

The formula for the number of comparisons between pairs of N people is: 

(N*(N-1))/2.

At 1596 pairs for N = 57  (99% chance)

99.9% ?? my choice would be 60 people

Wish You the Best in your Studies.

 .

Answer by ikleyn(52814) About Me  (Show Source):
You can put this solution on YOUR website!
.

For nice description of the  Birthday  Problem,  see this  Wikipedia article

https://en.wikipedia.org/wiki/Birthday_problem

https://en.wikipedia.org/wiki/Birthday_problem



For the  99.9%  probability,  this article gives the answer  70  people in the group.