Line Plots, Bar Charts & Pie Charts

Section 1 of 3

Line Plots & Bar Charts

Favourite colour of a group: Blue $5$, Red $6$, Pink $3$, Yellow $4$ — categorical, nominal data (words, no order).

Line plot

Stack an $\times$ for each item above its category. The tallest stack is the mode.

Bar chart

A bar for each category, height $=$ frequency. For categorical data leave gaps between bars. Label both axes.

You try

A survey of favourite colour gave: Pink $5$, Red $8$, Blue $3$, Green $7$, Yellow $2$. Draw it as a bar chart — what is the modal colour and how many people?

Tallest bar = mode; total = all frequencies.

Mode $=$ Red ($8$)

Total $= 5+8+3+7+2 = 25$

mode Red; $25$ people

Section 2 of 3

Pie Charts

Slices of 360°

A pie chart splits $360^{\circ}$ between the categories. Find the total, then $1$ item $= \dfrac{360^{\circ}}{\text{total}}$; each slice $=$ that angle $\times$ its frequency.

Worked example — draw a pie chart

Favourite colour: Red $5$, Blue $3$, Green $6$, Pink $4$. Find the angle of each slice.

Total $= 5+3+6+4 = 18$; $1$ person $= \tfrac{360}{18} = 20^{\circ}$

Red $= 20\times5 = 100^{\circ}$; Blue $= 60^{\circ}$; Green $= 120^{\circ}$; Pink $= 80^{\circ}$

$100^{\circ}, 60^{\circ}, 120^{\circ}, 80^{\circ}$

Section 3 of 3

Reading a Pie Chart

Work backwards

If you know how many one slice represents, use it to scale: (its people) $\div$ (its angle) gives people per degree, then $\times 360$ for the total.

Worked example — from angles to people

In an election pie chart: FG $150^{\circ}$, FF $120^{\circ}$, SF $30^{\circ}$, Others $60^{\circ}$. If $420$ people voted FG, find (i) the total who voted, (ii) how many voted Others.

$150^{\circ} = 420$, so $1^{\circ} = \tfrac{420}{150}$

(i) Total $= \tfrac{420}{150} \times 360 = 1008$ people

(ii) Others $= \tfrac{420}{150} \times 60 = 168$ people

$1008$ total; $168$ Others

That’s Class 5.

Line plots, bar charts (gaps for categories), and pie charts — drawing them and reading them back. Class 6: histograms and standard deviation.