When you are looking at data that has been sorted, describing which piece of information you are looking for can be quite difficult.

To get round this we use set notation.

What is a Set?

A set is just a list of pieces of information. They could be given as numbers, conditions, nonnumerical data. Just about anything.

Sets are always written inside a curly bracket, for example A = {1,2,3,4,5,6} or B = {multiples of 4}

The universal set:

When you look at a set question, sets are frequently given as conditions such as B = {multiples of 4}.

Because these are infinitly long, we need to limit this using the universal set.

This is just the set of numbers that the question is limited to, we use the symbol ε

**For example:**

ε = {Numbers from 1 - 20}

A = { Multiples of 3}

B = {Factors of 50}

This means A is the multiples of 3 up to 20

So A = {3,6,9,12,15,18}

We also have B being the factors of 50, but only up to 20.

So B = {1,2,5,10}

**What other Notation do we need?**

There are a number of set notations that you need to know for GCSE Maths.

**INTERSECTION:** This would be written as A**∩**B

This means all the values that are in A **and** B

**UNION:** This would be written as A**∪**B

This means all the values that are in A **or** B

**NOT:** This would be written as A'

This means all the values that are **not **in A

**Example:**

**ε = {Numbers from 1 - 20}**

**A = { Multiples of 2}**

**B = {Factors of 50}**

**Find the numbers that satisfy;**

**A∩B**

These are the numbers that satisfy both set A and B and that are less than 20

The only numbers that are both a factor of 50, a multiple of 2 and less than 20 are 2 and 10

**A****∪****B**

This means we want all the numbers that are either a multiple of 2 or a factor of 50 (and still under the limit of 21)

This gives us the numbers 1, 2, 3, 4, 5, 6, 8, 9. 10, 12, 14, 16, 18, 20

**A'**

Not A means all the numbers that aren't in set A.

This means the following numbers 1, 3, 5, 7, 9, 11, 13, 15, 17, 19