Data Interpretation • Topic 5 of 6

Line Graphs

A line graph shows how a quantity changes over time, with points joined by line segments. The steepness of each segment shows how fast the value is changing: a steep upward segment is a large increase, a downward segment a decrease, and a flat segment no change. Questions ask for the value at a given time, the change between two times (subtract the two values), the net change from start to end, or the interval with the greatest rise or fall (the steepest segment). Read values off the vertical axis carefully and watch the direction of change.

A line graph of temperature at four times of dayLine graph0102030141825216am9am12pm3pm

✅ Solved examples

1. Temperatures: 6am 14°, 9am 18°, noon 25°. What is the rise from 6am to noon?
25 − 14 = 11°.
2. Using the same data, the change from 6am to 9am?
18 − 14 = 4°.
3. Values 10, 14, 13, 20 over four hours. Between which hours is the biggest rise?
The jumps are +4, −1, +7; the largest is the 3rd to 4th (+7).
4. A graph starts at 30 and ends at 22. What is the net change?
22 − 30 = −8, a fall of 8.

✏️ Practice — try these, take hints as needed

1. Sales: Jan 200, Feb 260. What is the increase?
Subtract.
260 − 200.
—
60.
2. Temps 12°, 17°, 15°. What is the change from first to second reading?
Second minus first.
17 − 12.
—
5°.
3. Values 5, 9, 8, 16. Which step is the largest rise?
Steps: +4, −1, +8.
Largest is +8.
—
The last step (8 to 16).
4. A line goes from 50 down to 35. What is the net change?
End minus start.
35 − 50.
—
−15 (a fall of 15).
5. Readings 20°, 20°, 27°. What is the change in the second interval?
27 − 20.
—
—
7°.

📝 Topic test — 8 questions

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