jjykim

[Combinatorics Strategy]

I'm having trouble between deciding when order matters in a problem and when it doesn't.

For instance, #9 in the PSET questions in Chapter 4 of the Word Translation booklet, order matters whereas for #12, order doesn't.
I'm just confused as to how to decide when order does or dosn't matter.

[JonathanSchneider]

Great question. When order matters, we are dealing with a permutation. When order does not matter, we are dealing with a combination. For Problem #9, we are dealing with a permutation because we are asked to find the number of possible schedules, not the number of possible groups of teachers. For #12, however, we are dealing with the number of combinations of birds that can be fed, not the number of orders in which they can be fed.