# GCSE Statistics Chapter 7 Summary- Probability

After completing this chapter, you will be able to;

• Understand the meanings of the words ‘event’ and ‘outcome’
• Use a likelihood scale
• Put outcomes in order in terms of probability
• Put probabilities in order on a probability scale
• Understand the terms ‘random’, ‘equally likely’, ‘mutually exclusive’ and ‘exhaustive’.
• Understand and use measure of probability from a theoretical perspective and from a limiting frequency or experimental approach
• Compare expected frequencies and actual frequencies
• Use simulation to estimate more complex probabilities
• Use probability to assess risks
• Produce, understand and use a sample space
• Understand and use the addition and multiplication laws
• Use and calculate conditional probabilities
• Draw and use probabilities tree diagrams.
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First 242 words of the document:

Events and outcome
1.) A trial is the act of testing/ doing something.
2.) Outcomes are the possible results of a trial.
3.) An event is a set of one or more successful outcomes.
The meaning of probability
4.) Probability is a numerical measure of the chance of an event happening.
A probability of 0 means it is impossible for the event to happen
A probability of 1 means the event is certain to happen
5.) Probabilities can be written as fractions, decimals or percentages.
6.) When something is chosen at random, it means it is selected without a
conscious choice.
7.) When outcomes have the same chance of happening they are called equally
likely outcomes.
The probability of an event
8.) If all possible outcomes are equally likely, the probability of an event
=number of successful outcomes/total number of possible outcomes
Experimental probability
9.) The estimated probability that an event might happen
=number of successful outcomes/total number of trials
10.) As the number of trials increase in experiments and surveys the nearer an
estimate for the probability should be to the true value.
11.) Simulation is the imitation of the conditions of a situation by a theoretical
study.
12.) Cost of risk insurance= money at risk x risk assessment (p)
Sample space
13.) A list of all possible outcomes is called a sample space.
Venn diagrams

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A Venn diagram represents a sample space and may be used to calculate
probabilities. Set =s are represented as circles and common elements of the set
are represented by the areas where the circles overlap.
Mutually exclusive events
15.) Outcomes/ events are mutually exclusive if they cannot happen at the
same time.
16.) For two mutually exclusive events, A and B
P(A or B ) = P(A) + P(B)
17.) The addition law can be extended for three or more mutually exclusive

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Tree diagrams
26.) A tree diagram can be used to make calculations easier. Each branch of
the tree represents an outcome. The probability of thee outcome is written on the
branch.
27.) Sometimes one branch of a tree may end earlier than others.
Conditional probability
28.) Conditional probability is the probability of A given that B has already
happened.
It is written as P(A/B)
Multiplication law for events that are not independent