Factorial notation  Permutations and Combinations
Factorial notation
Lessons

2.
factorial notation: n! = n (n1) (n2) (n3) (n4) . . . . . (5) (4) (3) (2) (1)
by definition : 0! = 1 
a)
DOG

b)
MATH

c)
COMPUTER


4.
arrangement of words "with repititions" = $\frac{{n!}}{{\left( {{1^{st}}\;repetition} \right)!\;\;\;\left( {{2^{nd}}\;repetition} \right)!\;\;\;\left( {{3^{rd}}\;repetition} \right)!\; \ldots ..}}$
Determine the number of different arrangements of all the letters in the following words: 
5.
arrangement with restrictions: must deal with the restrictions first!

6.
seating arrangement