Question

The numbers $1,2,3,4,.....n$ are arranged in a random order. The probability that the digits $1$ and $2$ appear as neighbours in the order named is

• A. $\frac{1}{n-2}$
• B. $\frac{1}{n-1}$
• C. $\frac{1}{n}$
• D. $\frac{1}{n(n-1)}$

Answer 1

The correct option is C $\frac{1}{n}$

Create one packet of $1$ and $2$
and now arrange the $n-1$ numbers
The required probability $=(n-1)!/n!=1/n$