A line graph shows how something changes over time. Find the time on the bottom axis, go up to the point, then across to the scale. Check where the scale starts and what each gridline is worth. The change between two times is the difference between their values. A steeper segment means a faster change. An average change per week is the total change shared equally between the weeks: count the gaps between points, not the points.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- line graph
- points joined by lines to show change over time
- change
- how much a value went up or down between two times
- rate of change
- how much it changes in each step of time
Worked examples
The scale starts at 10 and goes up in 2s. A point is on the 4th gridline. What is its value?
- 1.Start at 10 and go up 4 gridlines of 2.
- 2.10 + 8 = 18.
= 18
Day 2 is 14 °C and Day 5 is 22 °C. By how much did it change?
- 1.Change = end − start.
- 2.22 − 14 = 8.
= 8
A plant was 10 cm in Week 1 and 30 cm in Week 5. Average growth per week?
- 1.Growth: 30 − 10 = 20 cm.
- 2.Week 1 to Week 5 is 4 gaps: 20 ÷ 4 = 5.
= 5
For parents
Method: Up from the label, across to the scale
What to say: Where does the scale start? How many gaps are there between those two points?
Common mistakes:
- Counts gridlines as ones and ignores the scale.
- Reads the point next to the one asked about.
- Reads as if the scale started at 0 when it starts higher.
- Uses the numbers along the bottom axis instead of the scale values.
- Gives the value at the end instead of the change.
- Gives the total change when a per-step (or single-step) change is asked for.
- Divides by the number of points instead of the number of gaps between them.
- Divides the final value instead of the change.
- Picks the highest point instead of the steepest rise.
- Picks the steepest segment even though it goes down.