in a minibus there are 16 seats for passengers. How many possible seating arrangements are there for 5 passengers?

the answer in the book is 210. no idea how you get that. isn't it a simple ?

furthermore in a similar question: there are 10 seats in the front row at a theatre, 6 people are shwon to this row. In how many different ways can they be seated if there are no restrictions? using gives the textbook answer.

and there is one more question, also similar. rory has to place colored pegs into holes in a board. he has 6 identical red pegs and the board has 10 holes. how many different arrangements are there for placing the 6 pegs and leaving 4 empty holes? using will give the textbook answer. however, these are identical pegs, not distinct people as in the previous 2 questions. using means that arrangements such as {red peg 1, then red peg 2}, and {red peg 2, then red peg 1} are counted as 2 different arrangements. shouldn't there be more calculations involved, such as ?