Year 12s: what will be the first way you research your future options? >>

unordered/ordered selection from set {1,2,3,4}?

List all unordered selections of 3 elements from the set {1, 2, 3, 4}.
List also all ordered selections of 3 elements from this set.

i'm not sure what i'm being asked here. is an ordered selection of 3 elements like, {1,2,3} and {2,3,4} where there are 3 elements in order? i've got a feeling there's a lot more to it than that though!

can anyone explain it at all? thank you :smile:

Reply 1

Hopple

You have a funny name for a girl. That or I should point out he's already taken.

You're right about an ordered selection, {1,2,3} is different from {2,3,1}, but they are the same unordered selection.

Reply 2

michael_douglas

Original post by Hopple

heh i'm not a michael douglas fan, it's just a song by neon neon :tongue:

so the ordered selections would be {1,2,3} and {2,3,4}, and the unordered selections would be {2,3,1}, {3,1,2}, {3,4,2} and {4,2,3}? or am i completely off the mark? thank you!

Reply 3

Hopple

Original post by michael_douglas

heh i'm not a michael douglas fan, it's just a song by neon neon :tongue:

so the ordered selections would be {1,2,3} and {2,3,4}, and the unordered selections would be {2,3,1}, {3,1,2}, {3,4,2} and {4,2,3}? or am i completely off the mark? thank you!

Wrong way round :tongue:

Unordered means they are only different if the numbers are different. {1,2,3}={1,3,2} but these are different from {1,2,4}, so in your list of distinct unordered selections, you'd write down {1,2,3},{1,2,4},etc.

Ordered means they are different if the order is different, so in the above example, you would write down all 3 as distinct ordered selections.

Edit: my bad, I just realised what you meant in your first post. An ordered selection is one in which you take note of the elements in it and their order, say like following a recipe. An unordered one is where you only care about what elements are in it, like making a smoothie.