Grade five, CIE IGCSE Maths

Revision Notes

What is a scatter graph all about?

Scatter graphs are used to see if there is a connection between two pieces of data.  For example a teacher may want to see if there is a link between grades in mathematics tests and grades in physics tests.  If there is a connection we can use a line of best fit to predict one data value (say the physics grade for example) from a known data value (maths grade).

What do I need to know?

You need to be able to plot and interpret a scatter graph.  They are sometimes called scatter plots or scatter diagrams but these all mean the same thing.  You also need to know about correlation (positive, negative) and how to draw and use a line of best fit.

Positive Correlation, IGCSE & GCSE Maths revision notes
Scatter Graphs Example 3, IGCSE & GCSE Maths revision notes
No Correlation, IGCSE & GCSE Maths revision notes
  1. Drawing a scatter graph

This is simply a matter of plotting points but be very careful which way round you are plotting them particularly when the values are very similar.

Scatter Graphs, IGCSE & GCSE Maths revision notes

eg John is buying a second hand car but is concerned about carbon dioxide (CO2) emissions.  He collects data about the age of a car the amount of CO2 the car emits.  His data is recorded in the table below.

Plot John’s results on a scatter graph and decide if there is a connection between age and CO2 emissions.  If there is use your graph to estimate how old a car emitting 104g/km would be.

2. Using a Scatter Graph

There is a positive correlation (as one value increases, so does the other) so add in a line of best fit and use this to answer the question.

SG2 Line of best fit, IGCSE & GCSE Maths revision notes

Notice that the line of best fit does not have to go through any of the data points.  If it does, it does. From the line of best fit that a car with emissions of 104 g/km would be about 7 years old.

Example

Scatter Graphs Example 1, IGCSE & GCSE Maths revision notes
SG3 Time Price, IGCSE & GCSE Maths revision notes
Scatter Graphs Example 2, IGCSE & GCSE Maths revision notes
SG4 Line of best fit, IGCSE & GCSE Maths revision notes
Scatter Graphs Example 3, IGCSE & GCSE Maths revision notes

Question

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