Question

Ajay, Ajith and Arun are friends. what is the probability that (in a non leap year ) All will have same birthday

Answer 1

The number of days in non-leap year = 365 days

The probability of two persons having same birthday would be $\frac{1}{365}$. This is because the birthday of the first person can be on any day ($\frac{365}{365}$) and the "possible outcome" of the second person's birthday would only be the one day out of 365 days.
Therefore, having these two events happening together is $\frac{365}{365}$ × $\frac{1}{365}$

Similarly, the "possible outcome" of having the same birthday for the third person is also one day out of 365 days. So the probability of three events happening together is  
$\frac{365}{365}$ × $\frac{1}{365}$ × $\frac{1}{365}$
= $\frac{1}{133225}$