Proportion Graphs
Represent proportional relationships using double number lines (two parallel number lines aligned at 0) and ratio tables; recognise that equivalent ratios generate straight lines through the origin when graphed
What a learner can do afterwards
- Plot pairs of proportional values on a coordinate grid and draw the straight line through the origin
- Explain why a directly proportional relationship always passes through (0,0)
- Read a proportion graph to find an unknown value — e.g. 'If 3 kg costs £6, how much does 5 kg cost?'
1 · Read
When two amounts grow together at the same rate, they are directly proportional. A ratio table lists matching pairs side by side. If 1 cinema ticket costs £4, then 2 tickets cost £8, and 3 tickets cost £12. Every pair in the table follows the same rate.
To turn a ratio table into a graph, plot each pair as a point on a grid: (1, 4), (2, 8), (3, 12). Draw a straight line through these points, and it will also pass through (0, 0). Now you can read off any value without working it out again. If 3 tickets cost £12, follow the line across to 5 tickets: it costs £20.
A directly proportional graph always passes through (0, 0), because zero tickets always cost zero pounds. If a graph starts anywhere else on the vertical axis, the relationship is not directly proportional.
Equal ratios plot as one straight line through zero, so a proportion graph lets you read off any amount at a glance.
2 · Watch
Take it off screen
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
17 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.