Question

P and Q are two friends standing in a circular arrangement with 10 more people. Find the probability that exactly 3 persons are seated between P and Q.

Answer 1

Fix $P$ at one point then number of places where $B$ can be seated is $11$.

Now, exactly three persons can be seated between $P$ and $Q$, so only two places where $Q$ can be seated.

So, $P=\frac{2}{11}$