http://www.ck12.org Chapter 3. An Introduction to Probability
You are taking a philosophy course that requires you to read 5 books out of a list of 10 books. You are free to select
any five books and read them in whichever order that pleases you. How many different combinations of 5 books are
available from a list of 10?
Solution:
Since considerations of order in which the books are selected are not important, we compute the number of combi-
nations of 10 books taken 5 at a time. We use the combination formula
Cnr=n!
r!(n−r)!
C^105 =10!
5!( 10 − 5 )!
= 256
There are 252 different groups of 5 books that can be selected from a list of 10 books.
Technology Note
The TI-83/84 calculators and the EXCEL spreadsheet have commands for factorials, permutations, and combina-
tions.
UsingtheTI-83/84Calculators
Press[MATH]and then choose PRB (Probability). You will see the following choices, among others:nPr,nCr,and
!The screens show the menu and the proper uses of these commands.
UsingEXCEL
In Excel the above commands are entered as follows:
• =PERMUT (10,2)
• =COMBIN (10,2)
• =FACT (10)
Lesson Summary
1.Inferential Statisticsis a method of statistics that consists of drawing conclusions about a population based
on information obtained from a subset or sample of the population.- Arandom samplingis a procedure in which each sample of a given size is equally likely to be the one
selected.