EQN-05-02

Reading Tables, Bar, Line & Pie Charts

Extract the right number from a data display and combine values without falling for the common traps.

~6 min read•Difficulty 2/5

Read the labels first

Before any calculation, identify: the title, the axis labels, the units, and the scale (does each gridline mean 1, 5, or 100?). Most data-question errors are misreadings, not miscalculations.

Bar and line charts

A bar chart compares separate categories; read each bar against the scale.
A line chart shows change over time; the steepest segment is the fastest change, and a falling segment is a decrease.

Pie charts $=$ parts of a whole

Each slice is a fraction of the total. If a slice is a percentage, the actual amount is:

amount = (slice percent /100) \times total

A 90° slice is one quarter (25%) of the circle; 180° is half.

Combining values

For "how many more", subtract the two read-off values. For "what percent", form the part-over-whole fraction and multiply by 100. Never guess between gridlines — use the given scale.

Diagram

A pie chart: each slice's angle is its share of 360°.

Worked examples

Example 1 (difficulty 1/5)

A pie chart shows that "Transport" is 20% of a monthly budget of 4000. How much is spent on transport?

◎ Predict the answer first:

Example 2 (difficulty 2/5)

A line chart shows sales of 30, 45, 40, and 60 over four weeks. Which week had the largest increase from the week before?

◎ Predict the answer first:

Tips

Spend the first few seconds reading the units and the scale — it prevents most errors.
For "largest change", compute consecutive differences, not the largest value.
On a pie chart, convert the slice to a fraction of the whole before multiplying by the total.

Common mistakes

Reading the highest point as the "biggest increase"

Why: The tallest bar/point draws the eye.

Fix: An increase is a difference between two points; compare the steps, not the heights.

Ignoring the scale and counting gridlines as 1 each

Why: Gridlines look like single units.

Fix: Check what one gridline represents before reading any value.

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