Диаграммы и графики

A picture is worth a thousand numbers

• The right chart makes patterns leap out. The wrong one hides them — or creates illusions.
• Choosing the right chart is a skill, not just a presentation trick.

Bar charts 条形图 and pictograms 象形图

• Bar chart: one bar per category; height $=$ frequency. Bars don't touch.
• Pictogram: a symbol stands for a number of items (e.g. one smiley $= 10$ people).

Each slice is its fraction of $360^\circ$: tea is $\tfrac{30}{120}\times360^\circ=90^\circ$

Pie charts 饼图

• A circle split into slices. Each slice is a fraction of $360^{\circ}$.

Stem-and-leaf 茎叶图 diagrams

• Keeps the digits of ordered data, with a key.
• Example: $23, 25, 31, 34, 37$ → stem $2$: $3, 5$; stem $3$: $1, 4, 7$.
• Advantage: you can read every individual value AND see the shape of the data.

Worked example — pie chart

• Of $120$ people, $30$ chose tea. Slice $= \dfrac{30}{120} \times 360^{\circ} = 90^{\circ}$.
• Of $160$ people, $40$ chose juice. Slice $= \dfrac{40}{160} \times 360^{\circ} = 90^{\circ}$.

Charts use scales just like number lines — always check what each unit represents.

Paired bars, stacked bars and keys

• Classes A and B record walkers 12,10 and cyclists 8,14. A dual chart has adjacent A and B bars for each travel method; a stacked chart has total height 22 for walkers and 22 for cyclists, with each class labelled in the key.
• A pictogram key of one symbol = 8 items makes half a symbol worth 4. For stem-and-leaf data $14,17,17,21,23$, write stem 1 with leaves 4,7,7 and stem 2 with 1,3; include key $1|4=14$.

You've got it