📚 Probability Basics: Outcomes, Events and Scales | 概率基础：结果、事件与概率尺度
Probability is one of the most practical topics in KS3 mathematics. It gives us a way to describe how likely an event is to happen, using numbers between 0 and 1. In everyday life we use words such as 'certain', 'impossible' and 'even chance', but in mathematics we make these ideas precise. This article reviews the key probability skills you need for Cambridge KS3, including theoretical probability, complementary events, expected frequency and experimental probability.
概率是 KS3 数学中最实用的主题之一。它让我们用 0 到 1 之间的数字来描述一个事件发生的可能性大小。在日常生活中，我们会使用 '一定'、'不可能' 和 '机会均等' 等词语，但在数学中我们要把这些想法变得精确。本文将复习剑桥 KS3 阶段所需的核心概率技能，包括理论概率、互补事件、期望频数和实验概率。
1. Understanding Probability | 理解概率
Probability measures how likely an event is to happen. The value always lies between 0 and 1 inclusive. A probability of 0 means the event is impossible, such as rolling a 7 on a standard six-sided die. A probability of 1 means the event is certain, such as rolling a number less than 7 on a standard die. The higher the probability, the more likely the event is.
概率衡量一个事件发生的可能性大小。其数值始终在 0 到 1 之间（含 0 和 1）。概率为 0 表示事件不可能发生，例如在标准六面骰上掷出 7。概率为 1 表示事件必然发生，例如在标准骰上掷出小于 7 的数。概率越高，事件就越可能发生。
Probability appears in many real-world contexts, from weather forecasts to games and insurance. When a forecast says there is a 70% chance of rain, it means the probability of rain is 0.7. In KS3 questions, you will often see probabilities given as fractions, decimals or percentages, and you should be able to move between these forms.
概率出现在许多现实情境中，从天气预报到游戏和保险。当天气预报说有 70% 的降雨概率时，意思是下雨的概率是 0.7。在 KS3 题目中，你经常会看到概率以分数、小数或百分比的形式出现，你应该能够在这些形式之间转换。
2. The Probability Scale | 概率尺度
A probability scale is a number line from 0 to 1. We can place events on this scale according to how likely they are. The main labels are impossible (0), unlikely (less than ½), even chance (½), likely (greater than ½) and certain (1). When you answer a KS3 question, you may need to match words to positions or explain why an event belongs at a particular point.
概率尺度是一条从 0 到 1 的数轴。我们可以根据事件发生的可能性把事件放在这条尺度的相应位置。主要标记是：不可能（0）、不太可能（小于 ½）、机会均等（½）、很可能（大于 ½）和一定（1）。在 KS3 题目中，你可能需要将词语与位置匹配，或解释某个事件为什么属于某个位置。
| Word 词语 | Meaning 含义 | Value or range 数值或范围 |
|---|---|---|
| Impossible | cannot happen | 0
Published by TutorHao | KS3 Mathematics Revision Series | aleveler.com
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