Probability
MYP Year 1 Mathematics — Probability
Probability is just a number that tells you how likely something is — nothing more mysterious than that. Every question your teacher throws at you boils down to one move: count what you want, count everything possible, divide. The marks disappear when students forget to simplify a fraction, mix up 'outcome' with 'event', or say 'unlikely' when they mean 'impossible'. Get the vocabulary precise and the counting careful, and this whole topic is arithmetic in disguise.
Overview: What This Chapter Is Really Testing
Probability questions at this level test three separate skills that examiners deliberately blend together: counting outcomes correctly, calculating a probability as a fraction (favourable ÷ total), and describing what that number means in words. Most lost marks come from skipping the describing part — students calculate correctly but can't say what it means for someone deciding whether to bring an umbrella.
- A single event is one thing happening once — flipping one coin, rolling one die.
- A combined event links two or more single events — flipping a coin AND rolling a die, or spinning a spinner twice.
- Dice, coins and spinners are the topic's 'lab equipment' because every section/face is equally likely — that assumption is what makes the counting method valid at all.
- The probability scale (0 to 1) is the language you use to describe any probability, whether it's a fraction, decimal or percentage.
The shape of the chapter
Command terms this topic loves
| Command term | What it demands | AO | Mark-earning move |
|---|---|---|---|
| List | Give all items with no explanation needed. | AO1 | Miss even one item (e.g. forgetting 2 is prime) and you lose the mark — order doesn't matter, completeness does. |
| State / Name / Identify | Give a short, direct answer — no working required. | AO1 | Writing a full explanation when only a value is asked wastes time but costs nothing; the reverse (no value when one is needed) loses the mark. |
| Calculate | Produce a numerical answer, normally as a fraction, showing the method. | AO2 | An unsimplified fraction like instead of can lose an accuracy mark on stricter mark schemes. |
| Describe | Explain what something means or looks like, in full sentences. | AO2/AO3 | A one-word answer ('sometimes') to a 'describe' question scores 0 — you must connect the probability value to the real-world meaning. |
| Compare | Identify similarities AND differences between two things, referencing both. | AO3 | Discussing only one spinner/event and never mentioning the other loses half the marks — you must compare, not just describe one side. |
| Explain | Give a reason, using mathematical justification (numbers, not just intuition). | AO3 | 'Because it feels more likely' scores nothing — you need the actual fraction or count as evidence. |
Key point
Overview