How can you tell they’ve got it: Probabilities Sum to One?

If they’ve got it, you’ll see things like: List all outcomes of spinning a 4-colour spinner and verify their probabilities add up to 1; Calculate P(not rolling a 3) as 1 − 1/6 = 5/6 using the complement rule; Spot an error in a probability table where the values don't sum to 1 and explain what's wrong. Or just try it together: 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?

Mathematics Probability Ages 10–11

Probabilities Sum to One

Your child knows all the chances in a situation add up to 1. If rain is 0.3 likely, then no rain is 0.7.

In curriculum terms

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

Ages are typical, not deadlines — follow your child’s pace. How to help at home →

How to tell they’ve got it

Tick these off as you see them — no test required.

List all outcomes of spinning a 4-colour spinner and verify their probabilities add up to 1
Calculate P(not rolling a 3) as 1 − 1/6 = 5/6 using the complement rule
Spot an error in a probability table where the values don't sum to 1 and explain what's wrong

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Try this together

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?

Where this sits on the map

Stuck here? Check the skills it builds on first. Confident? Here’s what it unlocks.

Builds on

The 0-to-1 Probability Scaleages 10–11The complement rule P(not A) = 1 − P(A) requires understanding probability as a number that lies between 0 and 1

Calculating Simple Probabilityages 10–11Using the complement rule is easier once students can calculate basic probabilities and see that favourable + unfavourable outcomes cover all possibilities

Probabilities Sum to Onethis skill · ages 10–11

Unlocks

Complementary eventsages 11–13The formal mutually-exclusive outcomes rule extends the simpler complement rule introduced at age 10-11

solid = must come firstdashed = helps

Curriculum alignment

Where this fits in the official school curriculum — our best automated guess, not yet checked by a person.

Show candidate curriculum codes · 3 ACARA

Australian Curriculum v9 candidate

AC9M5P01low confidenceYear 5 · Probability

list the possible outcomes of chance experiments involving equally likely outcomes and compare to those which are not equally likely

AC9M4P01low confidenceYear 4 · Probability

describe possible everyday events and the possible outcomes of chance experiments and order outcomes or events based on their likelihood of occurring; identify independent or dependent events

AC9M5P02low confidenceYear 5 · Probability

conduct repeated chance experiments including those with and without equally likely outcomes, observe and record the results ; use frequency to compare outcomes and estimate their likelihoods

These are candidate alignments generated by semantic matching — machine-suggested and unreviewed (v0.1), not official or verified mappings. For official curriculum content see australiancurriculum.edu.au, curriculum.nsw.edu.au and f10.vcaa.vic.edu.au. Don’t rely on them for registration or compliance purposes.

Nearby on the map

Calculating Simple Probabilityages 10–11 Experimental vs Theoreticalages 10–11 The 0-to-1 Probability Scaleages 10–11 Complementary eventsages 11–13

All Probability skills →