Combinations question (1 Viewer)

[Vampire]

I can't get this question. Any help would be appreciated.

How many ways can you make 4 groups of 2 from 8 people.

The answer is 105 but I don't know how to get it.

 

[Rorix]

8c2 * 6c2 * 4c2 * 2c2/4! = 105

 

[Vampire]

why do u divide by 4!

 

[Rorix]

because the order in which the groups are selected is irrelevant

 

[Vampire]

so? why exactly is it 4! - is it because there are 4 groups?

 

[Rorix]

yes
e.g. AB
CD
EF
GH
are the groups

(in order of selection)
AB
CD
EF
GH

is the same as CD AB GH EF
is the same as EF GH CD AB
and so on.

 

[Vampire]

using your advice would a question like 'how many ways can you split 8 people into 2 groups of 4' answer be (8C4*4C4)/2!
??

 

[Rorix]

*thumbs up*

 

[Vampire]

thx heaps Rorix