We know that the probability of an outcome is given by:
P(E)=Number of favorable outcomesTotal number of outcomes
Here, E is the event of A and B sitting together.
Let us draw the figure of their seating arrangement.
Since they are seated in a circular fashion, the order does not matter. Hence, A,B, and C will always sit next to each other.
∴ Number of favourable outcomes = 0
⇒P(E)=0
Hence, the probability that A and B will not sit next to each other will be 0.