Data points connected by straight lines to show trends over time.

A line graph plots values against a continuous scale, usually time, and joins consecutive points with straight lines. It is best for showing how a quantity rises, falls, or stays steady, and for comparing the trends of several series.

Reading a line graph

• Read the title, axis labels, legend, and units first.
• An upward slope means an increase, a downward slope a decrease, and a flat line no change.
• A steeper line means a faster change between the two points.
• Check whether the vertical axis starts at zero; otherwise changes may look larger than they are.
• In a multiple line graph, compare lines of the same series colour and look for where lines cross.

Common calculations

• Change: later value - earlier value.
• Percentage change: (new - old) / old x 100.
• Average: sum of the plotted values / number of points.
• Average rate of change: total change / number of intervals.
• Gap between two lines: difference of their values at the same point on the horizontal axis.

How to solve questions

1. Identify the series and the time points the question refers to.
2. Read each value accurately from the axis scale.
3. Apply the correct formula and keep units consistent.
4. Verify the result against the visible trend.