Chapter 49: Venn Diagrams and Notation

You can use a venn diagram to show frequencies in a probability question
This venn diagram shows the results when 50 people were asked whether they owned a dog or a cat
The rectangle represents everyone who was surveyed
The number in each section tells you how many people that section represents
Some people owned a dog and a cat so the ovals overlap
- The overlap can be represented by D n C
- 21+18+5 = 44 people owned a dog or a cat, you can write this as D u C

In maths a set is a collection of members or elements
The elements in a set could be numbers, words or letters
You can define a set in two different ways
- Listing the elements
- Using a rule

U means union. The union of two sets is the set of elements that belong to either set
N means intersection. The intersection of two sets is the set of elements that belong to both sides
e means the universal set. It represents all the elements you are allowed to consider in a question
A means not A or the complement of A. It is everything in e but not in A

Start by labelling two circles to represent the two sets
The write the x that are in both sets in the intersection of th two circles
Carry on filling in the venn diagram, and remember to write any leftover members outside the circles