Counting techniques:
A. General:
1. Sometimes the number of outcomes of your sample space is too
large to list and count. So counting techniques come in handy.
a. For example there are over 2.5 million five card poker hands.
B. Multiplication rule:
1. If the first event is done in x ways, and then a second event is
done in y ways, then the first event followed by the second event
has xy possible ways in which the events can be done.
a. For exampleThere
are five different roads that lead from your house to
your significant others house, and then four different roads
that lead to the movie theater. How many different routes
can you take to get to the movies?
All you gotta do is take the number of possible paths and
multiply them.
5 X 4 = 20 possible paths from home to the movies.
C. Combinations vs. permutations:
1. Permutation- is an ordered arrangement of k items from a larger
group of n possible choices,
a. Formula-
!
!
b. For exampleThe
abp decides to assign you a password consisting of 5
letters. You are learning statistics, so you want to see if you
learned anything. So you decide to see if you can calculate
the number of possible passwords:
It is definitely a permutation because the order of the letters in
your password is important. There are 26 letters in the
alphabet, and your password is 5 letters long so:
=
!
!
= 7893600 possible passwords!