probability (1 Viewer)

[charm13]

can anyone help me with probability? I really don't understand the ordered and unordered arrangements. If anyone can explain it to me it would be great!!!

 

[Becc]

in an ordered arrangement.. the order of the "objects" matters: for example.
if you have five people called A,B,C,D,E and you wish to order 3 of them:
A, B, C and B, C, A and B, A, C are all different and all matter.

in an unordered arrangement.. the order of the "objects" doesnt matter:
for example, if you have five people called A,B,C,D,E and you need to have three of them:
A, B, C covers all the other combinations of the same three letters.

does that make sense?

 

[KarmaKitten]

mmm calculators that do things for you

 

[malkin86]

Does your calculator have the nCr and nPr buttons?

n is the total number you can choose from and
r is the total number of choices you get

nCr is for choosing a combination (like lotto numbers) or a 'committee'. this is an unordered selection.

so if you're choosing a committee of two out of peter, paul, luke and john,
the committee of luke and peter is the same as the comittee of peter and luke.

nPr is used for arrangements (the mathsy word is permutations) - order is important. so this is an ordered selection.

you'd use this one for races, (or lotto strike) where luke coming first and peter coming second is different to the other way around.

 

[dark`secrets]

permutations - arrangements, putting things in order e.g "how many ways..in order."

combinations- no specific order and choosing from the sample space.

understand? if not just ask