Single events and relative frequency
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 6 practice questions, 1 real past-paper question with the answer explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- How likely is it?
- The probability scale
- Counting outcomes
Read the transcript of the teaching part
Last time
Before we start: last time, in Vector geometry, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
How likely is it?
Will it rain tomorrow? Will your team win? We put a number on how likely an event is, between zero and one. Zero means impossible, one means certain, and a half means even chance. You can find it by counting equally likely outcomes, or by doing an experiment and counting results. Both are in this lesson.
The probability scale
A probability is never negative, and never more than one. You may write it as a fraction, a decimal or a percentage. A fraction like three quarters is also zero point seven five, or seventy-five percent. An event that cannot happen has probability zero. One that must happen has probability one.
Counting outcomes
When all outcomes are equally likely, the probability is the number of favourable outcomes over the total number of outcomes. A fair die: the prime numbers are two, three and five. That is three out of six, a half. A bag with four red, five blue and three green counters: the chance of blue is five out of twelve.
How often it comes up
How often Cambridge has asked each part, counted by ExamYard from every past paper in its question bank: Relative frequency.
The whole chapter: Probability.
Chapter 29: Probability
- Single events and relative frequency 5 min
- Tree diagrams, conditional probability and Venn probability 5 min
Also for O Level Maths 4024
Which topics come up most in O Level Maths 4024 past papers, counted from every paper since 2004.