Line Graphs
Learn Line Graphs for GCSE Statistics with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA and Edexcel. Line graphs show how a quantity changes, often over time, by joining plotted points.
Free downloads
These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA and Edexcel specifications. Every worksheet comes with a full mark scheme.
Topic overview
A line graph plots points and joins them with straight lines, and is used for data collected over time.
Time is always placed on the horizontal axis. The vertical axis shows the variable being measured. Joining the points shows the trend, making it easy to see whether values are rising, falling or fluctuating.
The lines between points are an assumption rather than data. They suggest a steady change between the plotted values, which may not be what actually happened. Reading a value between two plotted points is interpolation and is reasonably safe; extending the line beyond the data to predict is extrapolation and is unreliable, because the trend may not continue.
Revision notes
Drawing a line graph
Time goes on the horizontal axis and the measured variable on the vertical axis.
Plot each point accurately and join consecutive points with straight lines. Label both axes and include units.
What the lines mean
The lines between points are an assumption of steady change, not measured data.
The actual values between the plotted points are unknown, so the line indicates the trend rather than recording what happened at every moment.
Interpolation and extrapolation
Interpolation reads a value between plotted points and is reasonably reliable.
Extrapolation extends the line beyond the data to predict, and is unreliable because the trend may not continue. Saying so is worth a mark whenever prediction is discussed.
Key points
- Line graphs show data collected over time.
- Time goes on the horizontal axis.
- Points are joined with straight lines.
- The lines show the trend, not measured data.
- Interpolation reads between plotted points.
- Extrapolation beyond the data is unreliable.
Worked examples
Example 1
A line graph shows sales of 120 in March and 180 in May. Estimate the sales in April by interpolation. [2 marks]
Working
Example 2
Explain why extrapolating from a line graph may be unreliable. [2 marks]
Working
Example 3
Explain what the straight lines joining points on a line graph represent. [2 marks]
Working
Common mistakes
Putting time on the vertical axis.
Time always goes on the horizontal axis.
Treating the joining lines as data.
They are an assumption of steady change between measured points.
Extrapolating without noting the risk.
Always say the trend may not continue.
Using a line graph for categorical data.
Line graphs are for data over time, not categories.
Exam tips
- Put time on the horizontal axis.
- Distinguish interpolation from extrapolation.
- Note that extrapolation is unreliable when predicting.
- Label both axes with units.
Key terms
- Line graph
- A graph of data over time with points joined.
- Trend
- The general direction in which values are moving.
- Interpolation
- Estimating a value between plotted points.
- Extrapolation
- Predicting beyond the range of the data.
Related topics
Written and reviewed against the current AQA and Edexcel specifications. Spotted an error? Let us know.