# Thread: Probability that 2 out of n have the same Bday

1. ## Probability that 2 out of n have the same Bday

Question :
What is the probability that atleast two out of n persons have the same birthday ? Assume 365 days in a year and all days are equally likely

2. Originally Posted by zorro
Question :
What is the probability that atleast two out of n persons have the same birthday ? Assume 365 days in a year and all days are equally likely
Pr(at least 2) = 1 - Pr(None) - Pr(1).

Now read this: Birthday problem - Wikipedia, the free encyclopedia

3. ## Still need some clarification

Originally Posted by mr fantastic
Pr(at least 2) = 1 - Pr(None) - Pr(1).

Now read this: Birthday problem - Wikipedia, the free encyclopedia
In the eq provided

Pr(at least 2) = 1 - Pr(None) - Pr(1).

1 - Pr(None) = Pr of all having the same Bday
Pr(1) = Pr of 1 having the same Bday

am i correct!!! then how is
(Pr of all having the same Bday) - (Pr of 1 having the same Bday) = (Pr of atleast 2)

please explain me i am dum!!!!!

4. Originally Posted by zorro
In the eq provided

Pr(at least 2) = 1 - Pr(None) - Pr(1).

1 - Pr(None) = Pr of all having the same Bday
Pr(1) = Pr of 1 having the same Bday

am i correct!!! then how is
(Pr of all having the same Bday) - (Pr of 1 having the same Bday) = (Pr of atleast 2)

please explain me i am dum!!!!!
At least two means more than one. Think about it.

5. ## Thank u Mr fantastic

Originally Posted by mr fantastic
At least two means more than one. Think about it.
Thank u Mr fantastic
Cheers