Ordered and Unordered Selections (1 Viewer)

[honky tonk]

In probability, there are ordered selections, such as the following:

Q. How many three letter words can be made from the letter {m,a,t,h}?

which is simple enough, just 4 x 3 x 2 x 1.

With unordered selections, such as the following:

Q. In how many ways can a committee of two be selected from the five people Andrew, Jane, Nicole, Richard and Trish?

you must use (5 x 4)/2.

I can understand the differences, but can someone please tell me an easy way to identify whether a question is asking for an ordered or unordered selection? I was away for the week we did this, and the textbook doesn't really help.

Thanks!

 

[JRasnier]

well the first does not say anything about how the order has to be like its not asking for anything really specific but then also if theres five ppl there cant be one person that is in the first place and also the second place, its just not physically possible, think of as a race, if a person comes first place, he cant be in third place also, well that goes for the first question, that is why when ur timesing, u are decreasing the number being timesed, but as the second one is asking for only two ppl out of the five, then its asking for only 2 ppl, but theres no set way, for example in ur question, Andrew and Jane are selected because u need to select two, because its not asking for a specific order, Andrew And Jane could be organised in an order of Andrew then Jane, or Jane then Andrew, so if for the second question....man im just confusing myself now


Well i got the same book your using,
'because Andrew and Jane is the same as Jane And Andrew, then (5x4) doesnt work, because it is counting Andrew and Jane, and also Jane And Andrew, as a different order...but since the order is different (no order necessary), the two ways of selecting jane and andrew are the same....as where in the first question it asking for the order, since all the letters are counted, and also is specifically asking for how many THREE LETTER WORDS, it is specifically asking for order, where as second question is asking for a COMMITEEE, not 'In how many ways can two people be selected from the five people Andrew, Jane, Nicole. Richard and Trish?' if they were asking this question then it would be (5x4)...

man i got a headache now, just confused the hell out of myself, i know what im talkin about, but just cant get it out properly, sorriez...

 

[honky tonk]

Thanks heaps, I understand it now. "Because Andrew and Jane is the same as Jane and Andrew, then (5x4) doesnt work, because it is counting Andrew and Jane, and also Jane and Andrew" summed it up very nicely.

 

[Rodrigue223]