1. AS 91267 4 credits External 2.12 Probability Methods

2. Note 1: Basic Probability Probability is how likely it is that an event will occur It is measured on a scale of 0 (impossible) to 1 (certain) It can be written as a fraction or a decimal

3. Note 2: Experimental Probability The results of experiments allow us to determine the relative probabilities from patterns in the past P(Event) = number of favourable outcomes total number of outcomes Example: There are 200 students at the local high school, 94 of these students are in the junior school. P(student is in the junior school) = 94 / 200 The probability that an event will not occur = 1 – P(event) P(student not in the junior school) = 1 – 47 / 100 = 53 / 100

4. Note 3: Two-way Tables A two-way table has rows which represent one variable and columns that represent another Each cell represents the frequency (or proportion) belonging to that particular row and column

5. Example: The following table shows the favourite subject of a group of year 9 students: EnglishMathsScienceTOTAL Boys12241147 Girls9301453 TOTAL215425100 A student is selected at random. Find P(a boy whose favourite subject is Maths) = P(Girl) = 24 / 100 53 / 100

6. Page 168 Exercise A