Lesson 2: Charts and Graphs – Pie, Bar, Histogram

👩🏽‍🏫 Introduction

Have you ever seen colourful charts in newspapers or social media? They’re not just pretty pictures—they tell powerful stories about data! 📈📊

In this lesson, you’ll explore three of the most common ways data is visually represented: bar charts, pie charts, and histograms. These tools make it easy to understand large amounts of data at a glance—whether it’s student test scores, survey results, or sports statistics. 🏀🎓

• 📊 Understand and interpret bar charts, pie charts, and histograms
• 📐 Learn how to construct each type of chart
• 📈 Apply them to real-world data

🧠 Key Concepts

📌 1. Bar Charts

• Used for comparing different categories.
• Each bar represents a value. Bars are separated by spaces.
• Height or length shows the size of the value.

Example Uses: Number of students in different classes, favorite fruits, etc.

📌 2. Pie Charts

• A circular chart divided into sectors (like slices of pizza 🍕).
• Each sector’s angle shows a proportion of the whole.
• Total angle =
  
• Sector angle =
  

📌 3. Histograms

• Used for grouped continuous data (like class intervals).
• Bars are joined—no spaces between them!
• Each bar represents a class interval, and its height shows frequency.

🔍 Worked Examples

1. 1. Example 1 – Bar Chart:
      Students’ favorite snacks:
      – Biscuits: 4 students
      – Chips: 7 students
      – Fruit: 3 students

      ✅ Bar chart:
      

1. 1. Example 2 – Pie Chart:
      A class of 30 students chose their favourite subjects:
      – Math: 10
      – English: 12
      – Science: 8

      ✅ Pie chart:
      

1. Example 3 – Histogram:
   Scores of 20 students are grouped as follows:
   – 0–9: 1
   – 10–19: 4
   – 20–29: 8
   – 30–39: 5
   – 40–49: 2

   ✅ Histogram:
   

✍🏽 Practice Exercises

🅰️ Section A – Bar Chart

1. The number of books read by students last term:
   Ama – 5, Kojo – 3, Efua – 6, Yaw – 4. Draw a bar chart.

🅱️ Section B – Pie Chart

1. Out of 40 students:
   10 like Music, 15 like Sports, and 15 like Reading.
   Draw a pie chart showing this distribution.

🅾️ Section C – Histogram

1. The ages of 15 children are grouped below:
   0–4: 2, 5–9: 5, 10–14: 6, 15–19: 2. Draw a histogram.

✅ Answers and Explanations

• A1: Bar chart with four bars for Ama (5), Kojo (3), Efua (6), and Yaw (4). Bars must be spaced.
• B1:
  Total = 40
  Music:
  
  Sports:
  
  Reading:
  
  ✅ Pie chart should have angles of 90°, 135°, and 135°.
• C1: Histogram bars for intervals:
  – 0–4: 2
  – 5–9: 5
  – 10–14: 6
  – 15–19: 2
  Bars should be touching (no gaps).

📌 Recap

• 📊 Bar charts compare categories with separate bars.
• 🥧 Pie charts show parts of a whole using angles in a circle.
• 📉 Histograms display grouped continuous data with joined bars.

💭 Reflection Prompt

Have you seen any data visualizations on TV, in newspapers, or on social media? Could you tell whether it was a bar chart, pie chart, or histogram? Why do you think visuals are often used instead of tables or numbers?