The number of ways six people sit in a six-passenger car is given by the number of permutations of 6 elements in 6 different positions ( seats), then
number of ways = number of permutations of 6 elements = 6! = 6 * 5 * 4 *3 * 2 * 1 = 720
Since the first person that sits can be on any of the seats , but then the second person that sits can choose any of 5 seats (since the first person had already occupied one) , the third can choose 4 ... and so on.
