Problem Solving

davo45 wrote:Thanks for the reasoning Cans. Please refresh my memory and tell me why the figure is divided by 24 and not 18.

Thanks.

For combinations, the formula is:

nCr (from n choose r)

n!/[r!(n-r)!] = 18!/[4!14!] = (18*17*16*15)/(4*3*2*1)


Whit

Frankenstein wrote:

[email protected] wrote:was this sentence is used to indicate that this is an combinations sum:

.how many different gropus of 4 applicants can be chosen by caomany to fill the postion if order dies not matter...

I just got a little confused and so please help me get rid of this confusion..

Hi,
how many different gropus of 4 applicants can be chosen by company to fill the position.
Choosing means selection(combination).

Order comes into play only when we talk about arrangement(permutation).

It is not the word 'chosen' that indicates we are dealing with a combination -- that is, that order does not matter. It is the fact that we are selecting 'groups' that tells us that the order of the people doesn't matter -- you still have the same group of people no matter what order you put them in.

There are many counting questions which use the word 'choose' but where order does matter. For example, I could ask how many ways you could choose a President and Treasurer from a group of 8 people. Then the order of the two selections clearly does matter, since if you change the order of the two people you select, you get a new President.

The word 'choose' has a technical definition in advanced math, but that definition sometimes conflicts with the way the word is used in day-to-day speech, and sometimes conflicts with the way the word is used on the GMAT. For GMAT purposes, it's best to forget the mathematical definition of the word 'choose' -- you should not assume, when you see the word 'choose' in a GMAT question, that order does not matter.