Probability
Maths: Edexcel IGCSE Higher, topic 6.3.1
Probability
The probability of an event is the likelihood of it happening. Probabilities are between 0 and 1 and the higher the probability, the more likely the event is to occur. Probabilities can be given as decimals, fractions or percentages.
Notation
- For a fair dice, P(6) means the probability of rolling a 6.
- For a bag of coloured balls, P(red) means the probability of a red ball being pulled out.
Relative frequency
- The relative frequency of an outcome during a probability experiment is an estimate of the probability of that outcome.
- The more trials performed during the experiment, the more accurate the estimate.
Sum of Probabilities
If all the possible outcomes of an event are listed then the sum of the probabilities of those events will be 1.
Probabilities add up to 1
- For any event:
- P(event happens) + P(event doesn’t happen) = 1.
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Rules
- The probabilities of a set of outcomes add up to 1 if:
- All possible outcomes are included
- Only one outcome can happen at a time.
Test yourself on Probability
Which of these are valid expressions for probability?
Which of these are valid expressions for probability?
Which of these are valid expressions for probability?
Which of these is true for a fair 6 sided dice?
Which of these is true for a fair 6 sided dice?