Introduction To Probability (Copy)

Cheat Sheet: Basic Probability (IGCSE Mathematics 0580 – CORE)
Topic: Probability Scale, Single Events, Complements

1. Probability Scale

• Probability is measured on a scale from 0 to 1.
• 0 means an event is impossible.
• 1 means an event is certain.
• Probabilities can be written as:
  • Fractions (e.g., 3/5)
  • Decimals (e.g., 0.6)
  • Percentages (e.g., 60%)

2. Probability of a Single Event

• Formula:

Probability=Number of favorable outcomesTotal number of outcomestext{Probability} = frac{text{Number of favorable outcomes}}{text{Total number of outcomes}}

3. Probability of an Event Not Occurring

• Formula:

Probability of not occurring=1−Probability of occurringtext{Probability of not occurring} = 1 – text{Probability of occurring}

4. Examples

• If the probability of raining today is 0.3,
  Probability that it does not rain = 1 – 0.3 = 0.7.
• If there are 5 red balls and 3 blue balls in a bag,
  Total balls = 8
  Probability of picking a red ball = 5/8
  Probability of not picking a red ball = 1 – 5/8 = 3/8

5. Probabilities Using Tables, Graphs, or Venn Diagrams

• For two sets in Venn diagrams:
  • Use simple counting to find favorable outcomes.
• The total of all probabilities in any situation must always add up to 1.

6. Important Tips

• Check whether the question asks for fraction, decimal, or percentage form.
• Probabilities cannot be negative or greater than 1.
• If you add probabilities of all possible outcomes, the sum should be exactly 1.

This cheat sheet fully covers all CORE-level probability basics for calculating single event probabilities and understanding complements.