Bar charts and time graphs
Interpret and present discrete and continuous data using appropriate graphical methods, including bar charts and time graphs
What a learner can do afterwards
- Read a time graph showing temperature changes over a day
- Present data about plant growth over weeks as a time graph
- Choose a bar chart for comparing categories or a time graph for measurements recorded over time, and explain the choice
1 · Read
You have read bar charts before. Each bar shows a value for one category. Bars help you compare separate groups, such as favourite colours.
A time graph can show measurements taken over time. Put time along the bottom and the measured value up the side. Label both axes and include units. Mark each reading where its time and value meet, then join the points in time order. Equal time gaps need equal spaces.
A plant measures 2 cm in week 1, 5 cm in week 2 and 9 cm in week 3. For its time graph, put weeks along the bottom and height in centimetres up the side. Plot the three readings and join them. These cells list the readings; they are not a time graph.
To read a time graph, find the time along the bottom. Move up to its point, then across to the value scale. Compare two readings to find whether the value rose, fell or stayed the same. Find the highest and lowest readings before finding their difference.
Compare recorded values: a larger number means a higher reading. Joined points help you follow changes but do not reveal unrecorded values between readings. Separate bars can also show readings at particular times. Joined points often make the pattern easier to follow. Counts, such as daily visitors, can change over time too.
A plant grows from 4 cm to 10 cm. Subtract the earlier height from the later height: 10 - 4 = 6 cm. If it first grows to 7 cm and then to 10 cm, its total growth is still 6 cm. The number line shows the height difference, not a time graph.
Bars compare categories. Time graphs connect readings in time order. Label the axes, use equal spacing and separate recorded values from values you do not know.
This lesson, question bank and flashcards were written for this dataset.
The readings, questions and flashcards were written for this dataset. The linked videos are by Khan Academy.
2 · Watch
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