🔢 Mathematics · Probability
Probabilities Sum to One
Understand that when all possible outcomes of a trial are listed, their probabilities must add up to 1; use this to find the probability of an event NOT happening: P(not A) = 1 − P(A); apply this shortcut to avoid counting all unfavourable outcomes directly
Typical age: 10–11 years
“If the probability of it raining tomorrow is 0.3, can your child work out the probability of it NOT raining — and explain why all probabilities in a situation must add up to 1?”
0 / 3 mastered
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Needs first
- The 0-to-1 Probability ScaleREQUIRED
The complement rule P(not A) = 1 − P(A) requires understanding probability as a number that lies between 0 and 1
- Calculating Simple Probability
Using the complement rule is easier once students can calculate basic probabilities and see that favourable + unfavourable outcomes cover all possibilities