n (> 3) persons are sitting in a row. Two of them are selected. Write the probability that they are together.

Let E denote the event that the selected persons are sitting together.


As 2 persons can be selected out of n in nC2 ways


Out of n persons we can select two persons sitting together in (n-1) ways.


Because we have to select only one person next person is going to be automatically selected.


We can’t select last person because no one is sitting next to him.


1 person out of n-1 persons can be selected in (n-1) ways.


P(E) =


Thus, P(E) =


2