Basic Probability

Task goals

• Place an event on a 0-to-1 probability scale and describe its likelihood using everyday language (impossible, unlikely, even chance, likely, certain).
• Distinguish theoretical probability (calculated from a sample space of equally likely outcomes) from experimental probability (based on trial results), and explain that experimental results vary between repeated trials even when the theoretical probability is fixed.
• Identify the sample space of a simple experiment (a die, a spinner, a deck of cards, a bag of counters) and use it to find a basic probability as favourable outcomes over total outcomes.
• Express a basic probability as a fraction, a decimal, and a percentage.
• Use the complement rule (P(not A) = 1 - P(A)) and recognise that mutually exclusive event probabilities add, while independent event probabilities multiply.
• Explain why a calculated probability outside the range 0 to 1 must be an error.