Outcomes
        In this lesson you will 
        - Be introduced to and use factorial notation. 
- Explore the formula for calculating the number of permutations obtained when r items are taken from a total of n items. 
By the end of this section you should be able to: 
        - Develop an understanding of factorial notation and apply it to calculating permutations and combinations. 
- Distinguish between situations that involve combinations and permutations. 
- Develop and apply formulae to evaluate permutations and combinations.
Prerequisites
        To be successful in this lesson, it would be helpful to know the following: 
        
        - The Fundamental Counting Principle.