Urn containg tickets problem From an urn containing n tickets numbered $1, 2, \dots, n$, $r$ tickets are drawn simultaneously and arranged in increasing order of their numbers $x_1<x_2<\dots<x_r$. Show that the probability that $x_i=s$ is
$$\frac{{s-1 \choose i-1}{n-s \choose r-i}}{{n \choose r}}$$
My attempt
From n tickets, r tickets can be drawn in ${n \choose r}$ ways. From the question, I understand that after drawing the tickets they should be arrangers in increasing order and so their  positions cannot be interchanged. Now I am unable to understand the meaning probability that $x_i=s$.
Please explain the meaning of the question and help me to solve. 
I hope someone can help. Thanks. 

For the $i$-th ticket (when arranged in order) to have value $s$, you would need $i-1$ values less than $s$, and $r-i$ values greater than $s$ (of course you must also choose ticket $s$--one way to do that).  The numerator of your expression shows how many ways there are to do each of these, and then they are multiplied together in accordance with the multiplication rule.
