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
Lesson
Set out your lesson
“Probabilities Sum to One means practising the idea at the table with counters or paper models and one clear check. We will demo once, then your child tries.”
Bring to the table
- 20 counters or beans
- Paper and pencil for recording sums
Extra for the adult
Worked example. 7 counters plus 5 counters make 12. Write 7 + 5 = 12.
Optional challenge. For Probabilities Sum to One, add one harder example after success.
What to notice. Keep one parent note: examples tried; results; support used. This session samples Probabilities Sum to One, not mastery.
Share and support
Family records and proof options
Keep a record of your learning
Save photos, notes, and attendance. Export a proof packet for compliance or portfolio reviews.
Practice this concept
Start practiceProbabilities Sum to One practice
Practice key ideas from Probabilities Sum to One.
Free · no login · no ads · Practice answers and completion are not saved. Parent observation remains the lesson record.
Learning resources
Extra practice links — they do not replace Gakuva’s teaching approach.
PhET Interactive Simulations · Practice link — not the full lesson
Plinko Probability
Before you open · source notes
Plinko Probability supports hands-on exploration for Probabilities Sum to One. Not every lab worksheet.
Free interactive page, no sign-in required for the tested path.
Before you openAsk the learner what they changed in the sim or page and what they observed.
Opening this link does not save learning or assess mastery.
Source, access and review notes
Public PhET Interactive Simulations page. An anonymous GET on 2026-11-12 returned HTTP 200 with no login or payment prompt for this URL. Opening the link does not save practice or assess mastery. An adult should preview and guide the learner.
PhET Interactive Simulations. “Plinko Probability.” External page; Gakuva does not copy, host, embed, or redistribute materials.
Unknown — link only
Check understanding
- 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
“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?”
Curriculum record
- Type
- Conceptual
- Subject
- Mathematics
- Domain
- Probability
- Age range
- Ages 10–11
Standards