persons are sitting in a row. Two of them are selected. Write the probability that they are together.

Explanation

The total number of ways of choosing 2 persons out of n is
`n_(​C_2)​`

After selecting two persons when the remaining`( n−2) `persons sit in a row `(n−1)`
places are created between them in which 2 persons can be arranged in `(n−1)_(​C_2)​.2! ways.`


So, the required probability
`=((n−1)_(​C_2)​)/(n_(​C_2))​=1−2/n​`