Random Experiment

A process, or an experiment is random means that

Sample space (표본 공간) • E.g. Coin toss → {heads, tails} ({앞면, 뒷면}) Event (사건) • E.g. 2 head obtained

Equally likely probability Formula

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Possibility Trees

Possibility trees (가능성 트리) • A tree structure is a useful tool for keeping systematic track of all possibilities in situations in which events happen in order. • The following example shows how to use such a structure to count the number of different outcomes of a tournament.

Q. Teams A and B play until one wins two games in a row or a total of three games.

a. How many ways can the tournament be played?

b. Assuming that all the ways of playing the tournament are equally likely, what is the probability that five games are needed to determine the tournament winner?

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The multiplication rule

Consider the following example.

How many ways are there to pair an input/output unit with a central processing unit?

⇒ As shown in the possibility tree, the same as the number of branches, 3 · 4 = 12

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