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

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) (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) (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.

RELATED QUESTIONS
How many people would you have to have in a group so that there is a probability of at... (answered by Boreal)
How many people would you have to have in a group so that there is a probability of at... (answered by ikleyn)
If you adhere to the requirements of the birthday problem (no twins, no leap year, an... (answered by ewatrrr)
How mnay people do you need to gather to be sure that at least two of them have a... (answered by richard1234)
in a group of n people (n<365) what is the probability two people have the same birthday... (answered by stanbon)
on a reality show a contestant must randomly choose enough people to go into a room so... (answered by stanbon)
A group of friends decides to buy a vacation home for $120,000, sharing the cost equally. (answered by mukhopadhyay)
in how many ways can you select two people from a group of 9 people? (answered by ewatrrr)
HOW MANY PEOPLE DO YOU NEED TO GATHER TO BE SURE THAT AT LEAST TWO OF THEM HAVE A... (answered by stanbon,josmiceli)