Primary 5 · Mathematics
P5 line graphs
A line graph shows change over time, and the commonest mistake is reading the steepest climb as the highest value. They are almost never the same point. Here is where a child picks the exciting part of the line instead of the answer.
- Level
- P5
- Usually taught
- Term 3
- Covers
- 1 concept
What changes at P5
In Primary 5, line graphs are about reading change over time. Your child reads a value off the graph, compares points, and describes how a quantity rose, fell or stayed flat between them.
The one idea a line graph adds over a bar graph is the slope between points. That slope is genuinely useful, and it is also where the reading goes wrong, because a steep line looks like a big value when it is not.
The sentence that costs the mark
From the graph, when was it hottest?
What the working usually does
steepestpart=2–3 pm
Picks where the line rises fastest. The 2 to 3 pm jump is the most dramatic part of the whole graph, so it draws the eye.
What the question asked
highestpart=6 pm
Picks where the line is highest. 6 pm is the top point, even though the line is nearly flat by then.
The steep climb really is the most eye-catching part, so 2 to 3 pm feels like the answer. But hottest asks for the highest temperature, which is the height of the point, not how fast the line is rising. Those are different places on the same line, and that difference is the whole reason a line graph exists.
| Time of day | Series 1 |
|---|---|
| 12pm | 28 |
| 1pm | 29 |
| 2pm | 30 |
| 3pm | 34 |
| 4pm | 35 |
| 5pm | 35 |
| 6pm | 36 |
The same question, worked properly
Read what hottest is asking
hottest = highest valueHottest means the highest temperature, which on a line graph is the highest point. It is asking for the greatest height, not the fastest change.
Do not pick the steepest climb
steep ≠ highThis is the step that fails. The 2 to 3 pm segment climbs fastest, but steepness is how quickly it warmed, not how warm it got. Choosing the steep part is the mistake this graph is built to catch.
Read the height at each point
highest point = 6 pm, 36°CLook across to the value at every point. The highest is 6 pm at 36°C, even though the line is nearly flat there. The top point is the answer, not the steep one.
How can you tell it has clicked?
You can check this straight off the graph together. Point at the steepest part and ask: is that the hottest, or just where it warmed up fastest? The question separates the two ideas.
If your child can say the hottest point is the highest one, wherever the line happens to be steep, they have understood what a line graph shows. If they go for the steep bit, that is the exact gap to close.
One thing to try tonight
Open a weather or step-count graph on your phone. Ask two questions about the same line: when did it go up fastest, and when was it highest?
They are usually different places, and that is the whole point of a line graph. Naming both, and keeping them apart, is the skill the P5 questions test.
What your child will meet in this topic
- Drawing Line Graphs
Most Singapore schools introduce this in Term 3, though schools do differ by a term either way. If your child’s school runs a different order, you can set it in the schedule on your dashboard.
What it leads to
Reading height as value and slope as rate of change is the foundation for every graph that follows. Distance-time and travel graphs in secondary school all rest on this one distinction.
A child who keeps steepness and value apart reads any graph correctly. One who blurs them reaches for the dramatic-looking answer, which is wrong more often than not.
The same topic in other years
It comes back each year and gets harder, so it helps to see what came before and what is coming.
More in Primary 5
Other topics in the same year, so you can see what sits either side of this one.
Struggling with the working rather than the topic itself? How to help your child with problem sums
See how your child is doing on this topic
StudyLah marks each step separately, so you can see whether it was the setup or the arithmetic that cost the mark.