a group of 5 people are seated in a circle with 6 available chairs, how many seating comvbinations are there and how is this number calculated?
You do the problem with them seating in a line (row) first. There are $\displaystyle 6!$ such ways. But now you divide by $\displaystyle 6$ because when they sit in a circle there are six ways round the circle to get the same seating.