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 nCr

r!rn

n!Crn )!(

(example)

Basic Probability

Permutations and Combinations:

Permutations: Each of all or part of a set of items.

change order → different arrangement

→ different permutations

Basic ProbabilityPermutations 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 nPr.

(n-r)!

n!

rnnnn

)1)...(2)(1)((Prn

(example)

Basic ProbabilityPermutations and Combinations:- Permutations (classes):

To calculate the number of considering classes of similar items.

A total of n items to be placed. n1 items are the same of one class, n2 are the same of the second class and n3 are the same as a third class.

n1+n2+n3=n

The number of permutations of n items taken n at a time:

!nnn

n!

321nn !!

P (example)