n (≥3) persons are sitting in a row. Two of them are selected at random. The probability that they are not together is
Answer & explanation
Correct answer: option 2
The total number of ways of selecting 2 persons out of n persons sitting in a row is "C2.
Number of ways in which two adjacent persons are selected from n persons sitting in a row = (n-1)
Hence, required probability = $\frac{^nC_2-(n-1)}{^nC_2}= 1-\frac{2}{n}$