Use the probability scale from 0 to 1; calculate probabilities of single events from equally likely outcomes; use the fact that probabilities sum to 1; and list combined outcomes using sample space diagrams.

What this dot point is asking

The Eduqas probability content begins with the basics: using the probability scale from $0$ to $1$, finding the probability of a single event from equally likely outcomes, using the fact that probabilities sum to $1$ (so the complement is $1 -$ the probability), and listing the outcomes of two combined events with a sample space diagram. These ideas underpin every later probability topic, and Eduqas tests them at both tiers with bags of counters, dice, spinners and cards. The sample space diagram for two dice is a recurring, reliable question.

The probability scale

Every probability is a number between $0$ and $1$, which can be written as a fraction, decimal or percentage.

A probability can never be negative or greater than $1$, which is a useful check: an answer outside that range signals an error. Eduqas may give the scale and ask you to mark an event's likelihood on it, or to convert between a fraction, a decimal and a percentage.

Single events from equally likely outcomes

When all outcomes are equally likely, probability is a simple ratio.

The phrase "at random" or "fair" tells you the outcomes are equally likely. From a bag of $3$ red and $7$ blue counters, P(red) $= \dfrac{3}{10}$. Always count the total carefully, including every category, before forming the fraction.

The sum of probabilities and the complement

Because some outcome must occur, all the probabilities add to $1$.

This is one of the most useful tools, because the complement is often far easier to count than the event itself. To find the probability of "at least one" of something, it is usually quicker to find the probability of "none" and subtract from $1$.

Sample space diagrams

A sample space diagram lists every outcome of two combined events, making counting systematic.

For two dice, the grid has $36$ cells, and many questions ask about the total of the two scores, so listing the totals in the grid lets you count outcomes for "total of 7", "an even total", and so on.

Why the basics matter

These foundations support tree diagrams, Venn diagrams and expected outcomes, all of which build on counting equally likely outcomes and using the sum-to-one rule. Because Eduqas weights reasoning across the paper, probability questions often ask you to interpret a result or justify a fairness claim, so understanding the scale and the complement, not just the arithmetic, is what secures full marks.