probability and combinatorics mixed question A bus follows its route through nine stations, and contains six passengers. What is the probability that no two passengers will get off at the same station? 
no detailed solution is required here but an idea of the general line of thought could be nice...

This is an occupancy problem.  You need to count the number of ways that 6 balls can get put into 9 sacks, such that each sack has at most 1 ball in it.  Hint: since at most one person gets of at each bus stop, you are putting an order on the bus stops.
