PERMUTATION:
The number of arrangement of r
items taken from n distinct items. Order of
arrangement is important in permutation.
_{n}P_{r} =
P(n, r) = n!/(nr)!
Question:
How many three letter words can be formed by using the
letters of
A, B, C, D, E? Each letter must be used once.
_{5}P_{3} =
5!/(53)! = 60
ABC, ACB, BAC, BCA, CAB,
CBA are all different words although the same letters are
used. Therefore all of the words should be considered.
ANOTHER WAY TO SOLVE THIS
PROBLEM: First letter
can be chosen in 5 ways
Second letter can be chosen in 4 ways
Third letter can be chosen in 3 ways
5 x 4 x 3 = 60 ways


COMBINATION:
The number of selection of r
items taken from n distinct items. Order of selection
is not important in combination.
_{n}C_{r} =
n!/[(nr)! r!]
Question:
How many ways can a three member committee be set up by the
persons of A, B, C, D, E?
A for Ashley
B for Brandon
C for Carol
D for Daniel
E for Emily _{5}C_{3} =
5!/[(53)! 3!] = 10
Committee consisting of ABC, ACB, BAC, BCA, CAB, CBA are all
the same for the combination. Therefore, only one will
be considered. 