IGCSE Maths / Working with data
Bar charts, pie charts and pictograms revision notes
Edexcel International GCSE Maths (4MA1), chapter 19: Working with data, specification point 6.1a-f. Free lesson.
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Bar charts show counts, pie charts show shares of a whole, and pictograms show counts using symbols. Knowing what to read in each chart helps you interpret data and calculate pie chart angles correctly.
What each chart shows
Read what the chart measures first. A bar chart shows how many are in each group, so the height of each bar gives its frequency, or count. A pie chart shows each group’s share of the whole, so you compare the size of the slices. A pictogram uses symbols to represent items, so you must read its key before counting. Use a bar chart to compare counts between groups. Use a pie chart to compare proportions, not counts. Without the total, you cannot tell how many people a slice represents. Use a pictogram by checking the key, then counting the symbols.
How to find a pie chart angle
A full circle is 360°, shared between everyone in the whole group. Find the degrees for one person first, then multiply by the number of people in the category. The angle represents the category’s share of the total. The angles for all the slices must add up to 360°.
How to read a pictogram key
The key tells you how many items each whole symbol represents. A fraction of a symbol represents the same fraction of the key’s value. For example, half a symbol means half the number of items shown by one whole symbol. Work out the value of the whole symbols first. Then find the value of any part-symbols and add the amounts.
Compare shares carefully
A bigger pie chart slice does not always mean more people. It means a bigger share of that particular whole. A large share of a small group can be fewer people than a smaller share of a much larger group. Half of 20 people is 10. A quarter of 100 people is 25. Use pie charts to compare shares and bar charts to compare counts.
More lessons in Working with data
- Two-way tables and reading statistical diagrams
- Mean from a frequency table
- Estimated mean and modal class for grouped data
- Frequency density
- Drawing a histogram
- Reading frequencies from a histogram
- Completing a histogram from a part drawn graph
- Estimating a frequency within a class
- Building a cumulative frequency table
- Plotting a cumulative frequency diagram
- Reading values from a cumulative frequency graph
- Estimating how many are above or below a value
- Estimating the median from a cumulative frequency diagram
- Estimating the interquartile range from a cumulative frequency diagram
- Comparing two cumulative frequency distributions
- Mean, median, mode and range
- Quartiles and the interquartile range for discrete data
- What a measure of spread tells you
- Using the interquartile range to compare distributions