Line graphs (age 10+)
Interpret and construct pie charts and line graphs; use these to solve problems
What a learner can do afterwards
- Read values from a line graph showing temperature over a day and identify trends
- Construct a pie chart from given data by calculating sector angles
- Use a pie chart to determine the actual quantity represented by each sector given the total
The lesson
A line graph shows how something changes over time. Each dot is a value at a certain time, and the dots connect with a line. When the line goes up, the value is increasing. When it goes down, the value is decreasing. When the line is flat, the value is staying the same.
A line graph tracks temperature through a day: 10°C at 6am, 14°C at 9am, 20°C at 12pm, 22°C at 3pm, then 18°C at 6pm. The line rises all morning, keeps climbing into early afternoon, then turns and falls toward evening. The warmest point on the graph is 3pm, right where the line changes direction.
A pie chart shows how a whole amount splits into parts. The whole circle stands for the total, and each slice, called a sector, stands for one part. You already know a full turn is 360°, and that's exactly how much a full circle holds. To find a sector's angle, work out what fraction of the total that part is, then multiply by 360°.
24 children picked a favourite fruit: 12 chose apples, 6 chose bananas, and 6 chose grapes. Apples are 12 out of 24, which is half, so that sector gets half of 360°, which is 180°. Bananas and grapes are each a quarter, so each of those sectors gets 90°.
Once you know a sector's percentage or fraction, you can find the real quantity, too. Just multiply the total by that fraction. If a $40 budget pie chart shows 25% spent on Fun, that's 25% of $40, which is $10.
A line graph shows change over time; a pie chart shows a whole split into parts, each sector sized by its fraction of 360°.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.