Question

The probability that in a group of $N(<365)$ people at least two will have the same birthday, is________ .

Answer 1

We have $2$ persons $p_1$ and $p_2$ out of $365$ days.

$p_1$ can have $365$ chances

$p_2$ can have $365$ chances ${365}^2$

$p_1{p}_2$ have same birthday $365$

$\begin{array}{c}{p}_{1}canhave365chances\\ p_{2}canhave365chances\end{array}\}{365}^2$

$p\left(A\right)=2$ persons have same birthday $=\frac{365}{{365}^2}=\frac{1}{365}$