Complementary events

Recognise that an event and its complement have probabilities adding to 1, and use this to find probabilities quickly, including ‘at least one’ problems.

⏱ 18 min❓ 9 questions

What you'll be able to do

✔I can describe the complement of an event
✔I can use P(not A) = 1 − P(A) with fractions, decimals and percentages
✔I can use the complement to find the probability of ‘at least one’

How this works

1Read the short explanations first — they teach you what you need before each question.
2Answer each question, then tap Check. A right answer moves you on automatically; if it's wrong, you'll see a friendly explanation of why.
3Finish all 3 steps to see your score — sign in and subscribe to unlock the full lesson and save it.

What's inside

9 questions and 1 quick teaching card, including:

🔢Number answer — Work out the answer and type the number.
🔘Multiple choice — Tap the answer you think is best, then check it.

👪Grown-up tip: sit alongside younger learners for the first few lessons. Read the questions together and chat about the explanations — that's where the real learning sticks.

Curriculum: AC9M8P01