🔢 Mathematics · Probability

Calculating Simple Probability

Calculate the probability of a simple event with equally likely outcomes using the formula: probability = number of favourable outcomes ÷ total number of possible outcomes; express the result as a fraction in its simplest form; apply to rolling dice, drawing from bags, and other simple chance situations

Typical age: 10–11 years

“If there are 3 red and 7 blue balls in a bag, can your child work out the probability of picking a red one and express it as a fraction in its simplest form?”

0 / 3 mastered

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Needs first

The 0-to-1 Probability ScaleREQUIRED
Calculating probability using favourable/total outcomes requires understanding probability as a number on a 0-1 scale
Equally Likely OutcomesREQUIRED
The probability formula only applies to situations with equally likely outcomes — this concept must be secure first

Unlocks next

Probabilities Sum to One
Using the complement rule is easier once students can calculate basic probabilities and see that favourable + unfavourable outcomes cover all possibilities
Experimental vs TheoreticalREQUIRED
Comparing experimental results with theoretical predictions requires being able to calculate the theoretical probability first
The Probability ScaleREQUIRED
The formal KS3 treatment of probability as a 0-1 scale with fairness and equally-likely outcomes formalises what was practised in the age-10-11 calculation node