<p>I don't know if there is a thread over this already....but I still don't get how to do permutations and combinations.</p>
<p>Anyone want to help me understand it?</p>
<p>permutations:</p>
<p>5! is 5x4x3x2x1 -- that's it</p>
<p>combinations</p>
<p>combinations are permutations (5x4x3x2x1) divided by a permutation of a particular possibility (1x2)</p>
<p>I can't think of an example of when combinations are used...but that's all you really need to know</p>
<p>That's the thing...I know what they are; I just don't know when to use them in terms of like word problems.</p>
<p>ok guides:
and= multiply the comb. perm whatever
or= add</p>
<p>array, arrange etc= permutation
possible groups=combinations</p>
<p>thats more or less it</p>
<p>like when you're typing it in the titanium you do like nCr or nPr (or w/e)...and you have to type like nCr(total, number)...but then sometimes you have to like divide by like other nCrs ....</p>
<p>JyankeesSS2~
Permutations is not sth like 5!=5<em>4</em>3<em>2</em>1=120. That is 5 factorial. The ! means factorial. </p>
<p>Think of it this way, in permutations order matters but in combinations it doesnt.</p>
<p>For TI 89~ press 2nd and 5 which brings up math. Under probability select NCr for combinations. This will come up-- NCr(type total #, the number you want) and enter. This will give you the answer.</p>
<p>hmm that would be for probablitiies, where you divide the possible combinations for the event by the possible combinations of the sample space</p>
<p>srsti: permutations are with factorials, where the order matters. From there on we can go into permutations with repetitions etc, but yes the factorial is the basis so JyankeesSS2 isn't wrong really.</p>
<p>megaman~ The formula for permutations does have factorials. But it isn't n!.
It is n!/(n-r)!. For permutations with repititions it is n!/(p! q!). </p>
<p>Even though factorials are the basis, you can't go on and simply say that permutations is n! . It is giving the wrong idea.</p>
<p>ok look this is how it is, Permuations are Used when the order of the objects MATTERS , like for example you are aranging four books on a shelf or something, and you want to see the number of possible arrangments, so you do 4 P 4 Which IS 4!/(4-4)! Which IS 4! = 24 .
combinations however is used when the order DOESNT matter, like for example when you are drawing cards out of a 52 Card Deck, and lets say for example u want to find out the Possible combinations of a 4 Hand deck. u would do 52 C 4 , Which iS 52!/(4!*48!) which is =270725 possible combinations
Also Note that nCr=cPr/r! , Where the Extra Divison of the r! , elimnates the ORder.</p>