Question

$n$ persons are to sit in a row at random. The probability that two particular persons are together

• A. $\frac{3}{n}$
• B. $\frac{2}{n}$
• C. $\frac{1}{n}$
• D. $\frac{4}{n}$

Answer 1

The correct option is B $\frac{2}{n}$

n persons are to sit in a row at random.
Take 2 person take as one group, then for two particular persons are together the ways is = 2! (n-1)!
Total ways for n person are to sit in a row at random = n!
The probability that two particular persons are together $=\frac{2!(n-1)!}{n!}=\frac{2}{n}$