Theoretical Probability
Maths: Edexcel IGCSE Higher, topic 6.3.2
Theoretical Probabilities
We can work out the theoretical probabilities involved in an experiment without having to do the experiment itself.
Formula
- This is true assuming all outcomes are equally likely.
Example
- P(rolling even number on fair die) = 3 ÷ 6 = 1⁄2
- There are 3 even numbers it could be (2,4,6) and there are 6 possible outcomes overall (1,2,3,4,5,6).
Multiple Events
A spinner has 5 possible outcomes, a dice has 6 possible outcomes and picking a card from a deck of cards has 52 possible outcomes. What is the total number of ways to spin the spinner, roll the dice and pick a card?
Outcomes from the spinner
Outcomes from the dice
Outcomes from picking a card
Multiply them together
This is our answer
Test yourself on Theoretical Probability
There are 3 lions and 5 bears at a zoo. One animal is chosen at random. What is the probability the animal chosen is a lion?
There are 3 lions and 5 bears at a zoo. One animal is chosen at random. What is the probability the animal chosen is a bear?
There are 3 goalkeepers and 10 defenders in a football squad of 44. One player is chosen at random. What is the probability a goalkeeper is chosen?
There are 3 goalkeepers and 10 defenders in a football squad of 44. One player is chosen at random. What is the probability a defender is chosen?
3 goalkeepers, 10 defenders and Peter Crouch are in a football squad of 44. One player is chosen at random. What is the probability Peter Crouch is chosen?