Direct proportion graphs
The Maths Habit
Which is the odd one out? Why?
B: it does not start at 0.
C: it is not a straight line.
A: it is the only straight line from 0.
Across first, then up.
- 1Which point is (2, 6)?A
- 2Which point is (6, 2)?B
- 3Which point is (5, 4)?D
- Direct proportion
- Two amounts that grow together. Double one and the other doubles.
- Origin
- The point (0, 0), where the axes meet.
- Plot
- Mark a point on a grid with a small cross.
- Axis
- A number line along the bottom or the side of a graph.
1 kg of pears costs £2. Draw the graph.
| kg | 0 | 1 | 2 | 3 | 4 |
| Cost (£) | 0 | 2 | 4 | 6 | 8 |
1 cup costs £5. Draw the graph.
| Cups | 0 | 1 | 2 | 3 | 4 |
| Cost (£) | 0 | 5 | 10 | 15 | 20 |
1 kg of pears costs £2. Draw the graph.
| kg | 0 | 1 | 2 | 3 | 4 |
| Cost (£) | 0 | 2 | 4 | 6 | 8 |
1 box holds 10 crayons. Draw the graph.
| Boxes | 0 | 1 | 2 | 3 | 4 |
| Crayons | 0 | 10 | 20 | 30 | 40 |
1 kg of pears costs £2. Draw the graph.
| kg | 0 | 1 | 2 | 3 | 4 |
| Cost (£) | 0 | 2 | 4 | 6 | 8 |
1 bus ticket costs £4. Draw the graph.
| Tickets | 0 | 1 | 2 | 3 | 4 |
| Cost (£) | 0 | 4 | 8 | 12 | 16 |
1 kg of pears costs £2. Draw the graph.
| kg | 0 | 1 | 2 | 3 | 4 |
| Cost (£) | 0 | 2 | 4 | 6 | 8 |
1 bag holds 3 apples. Draw the graph.
| Bags | 0 | 1 | 2 | 3 | 4 |
| Apples | 0 | 3 | 6 | 9 | 12 |
Direct proportion? Thumbs up or thumbs down.
A straight line?Through (0, 0)?
Answer sheet
2 pens cost £6. Fill in a table for 0 to 4 pens.
0, 3, 6, 9, 12A taxi costs £3 to start and £2 a mile. Is it direct proportion?
No: 0 miles costs £31 pen costs £3. The graph stops at 4 pens. Find the cost of 6 pens.
£18 (£12 + £6)
1 pen costs £3. Draw the graph.
a line from (0, 0) to (4, 12)Pens 0 1 2 3 4 Cost (£) 0 3 6 9 12 1 bag holds 4 apples. Draw the graph.
a line from (0, 0) to (4, 16)Bags 0 1 2 3 4 Apples 0 4 8 12 16 Is your graph in question 2 direct proportion? Why?
Yes: it is a straight line through (0, 0).