How can you tell they’ve got it: Complementary events?

If they’ve got it, you’ll see things like: Verify that probabilities of all outcomes listed for a spinner sum to 1; Calculate the probability of NOT rolling a 6 as 1 − 1/6 = 5/6; Identify an error in a probability distribution where the values do not sum to 1. Or just try it together: If a spinner has three sections and one has a probability of 0.4 and another has 0.35, can your child work out the probability of landing on the third section without being told?

Mathematics Probability Ages 11–13

Complementary events

Your child knows all the chances add up to 1. On a spinner where two parts are 0.4 and 0.35, the third is 0.25.

In curriculum terms

Understand and apply the rule that probabilities of all mutually exclusive outcomes sum to one; use this to find the probability of a complementary event (P(not A) = 1 − P(A))

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.

Verify that probabilities of all outcomes listed for a spinner sum to 1
Calculate the probability of NOT rolling a 6 as 1 − 1/6 = 5/6
Identify an error in a probability distribution where the values do not sum to 1

🖨 Print this page to keep the checklist — it prints beautifully.

Try this together

If a spinner has three sections and one has a probability of 0.4 and another has 0.35, can your child work out the probability of landing on the third section without being told?

Where this sits on the map

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

Builds on

Probabilities Sum to Oneages 10–11The formal mutually-exclusive outcomes rule extends the simpler complement rule introduced at age 10-11

The Probability Scaleages 11–13Probabilities summing to 1 builds directly on understanding the probability scale

Complementary eventsthis skill · ages 11–13

Unlocks

Sets & Venn Diagramsages 12–14Enumerating sets for probability requires understanding that all outcomes sum to 1

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.

This skill sits outside the F–6 Australian Curriculum — no candidate code matched (v0.1). No NSW K–6 outcome code matched (v0.1). No Victorian Curriculum 2.0 code matched (v0.1).

Nearby on the map

Experimental probabilityages 11–13 The Probability Scaleages 11–13 Calculating Simple Probabilityages 10–11 Experimental vs Theoreticalages 10–11

All Probability skills →