Probability Help...

[paradigm2200]

I am taking all these practice test (TopScore and Dat Acheiver) and they seem to place a heavy emphasis on the more advance type of probability questions...

Can anyone be so kind enough to explain when to use combinations and/or permuations...

Are questions like these even very significant on the real dat..



thanks

 

[INFNITE]

combinations: when order doesn't matter. For example, pick 3 letters out of A,B,C,D,E, ABC, CBA, BCA, ACB, BAC, CAB count as one combination. when you use permutations, there would be 6 selections because order matters in permutation.