permutations and combinations

[sonoma1993]

For this math exam I just took online, I had these two problems that deal with permutations and combinations. How do you know which one to use?

here the two problems I had

This term there are eight candidates for three student senate seats, how many diffrent ways can the seats be chosen?

anwser are

24
8
3
56
336 - I chose this one

I used permutations for this one

here the other one

The total student senate consists of 12 members, an internal vote elecs a president, vice president and secretary among the 12 members. In how many diffrent ways can these offices be filled?

1320
36
220 - I chose this one
12

I used combinations for this one.

 

[Einz]

Combinations are for when order doesn't matter, and permutations are for when order does matter. You got the two bassackwards. The first one you should have used combinations and the second you should've used permutations.

 

[Cobalt]

The answer to the first one is 56, use combination when order DOESN'T matter. The answer to the second question is 1320. That is permutation, because the order of the candidates does matter - Pres, Vice Pres, Secretary. Hope this helps.

EDIT: Beat to it.

 

[DaShen]

8!/(8-3)! = 336


Wouldn't the second one be
12!/(12-3)! = 1320? Am I missing something here?

**EDIT**
Oops

8!/(8-3)!3! = 56 Combinations

 

[sonoma1993]

Originally posted by: Einz
Combinations are for when order doesn't matter, and permutations are for when order does matter. You got the two bassackwards. The first one you should have used combinations and the second you should've used permutations.

when a group of people choose among there selves for the 3 positions, it would be permutations?