1. Basic Probability Permutations and Combinations: -Combinations: -The number of different packages of data taken r at time from a data set containing n items. The order of items is inconsequential. The number of taken r at a time (r ≤ n) is written n C r (example)

2. Basic Probability Permutations and Combinations: Permutations: Each of all or part of a set of items. change order → different arrangement → different permutations

3. Basic Probability Permutations and Combinations: -Permutations: A total of n distinguishable items to be arranged. r items are chosen at a time (r ≤ n). The number of of n items chosen r at a time is written n P r. (example)

4. Basic Probability Permutations and Combinations: -Permutations (classes): To calculate the number of considering classes of similar items. A total of n items to be placed. n 1 items are the same of one class, n 2 are the same of the second class and n 3 are the same as a third class. n 1 +n 2 +n 3 =n The number of permutations of n items taken n at a time: (example)