Probability OCR Stage 6

Probability In an experiment, things that can happen are called possible outcomes Each of these has a possibility

Probability of an event happening Probability = Required Outcome Total Possible Outcomes i.e. The number of required outcomes divided by the total number of possible outcomes

Getting a 4 on a single dice There is 1 required outcome – a four There are 6 possible outcomes P(4) = 1 The answer may be written as a fraction, decimal or percentage 6 NEVER as “one out of six” The P says, “The probability of”

The probability of not getting a 4? There are five numbers on the single dice that are not a 4 There are six possible outcomes So, P(Not getting a 4) = 5 6

1/6 + 5/6 = 1 The total probabilities of any event have a total of 1 It is important that you notice that the two probabilities add together to give 1 The total probabilities of any event have a total of 1 1/6 + 5/6 = 1 Probability of not getting a 4 on a single dice Probability of getting a 4 on a single dice

Sum of all probabilities equal 1. Example The probability of a football team’s results in the next match are: P(Win) = 0.3 P(Lose) = 0.5 What is the probability of a draw?

Remember the total of all the probabilities is 1 The team must win, lose or draw. P(Win) + P(Lose) + P(Draw) = 1 0.3 + 0.5 + P(Draw) = 1 0.8 + P(Draw) = 1 P(Draw) = 0.2 This is 0.5 This is 0.3

Mutually Exclusive events Can NOT happen at the same time Examples A HEAD and a TAIL when coin is spun A 6 and an odd number when die rolled A level 5 and a level 6 on a SAT paper

Example Sam and Pete play chess P(Sam wins) = 0.4 P(Pete wins) = 0.3 What is P(Draw) ? 0.4 + 0.3 + P(Draw) = 1 0.7 + P(Draw) = 1 P(Draw) = 0.3

Exercises – to be completed next lesson OCR Stage 5/6 Text, Stage 6, Chapter 4, Page 182 Ex 4.1A Ex 4.1B Ex 4.2A Ex 4.2B