P6 Mathematics - Term II

Topic 6: Data Handling

Lesson 2: Pie Charts - Construction and Interpretation

Duration: 45 minutes

Learning Objectives

By the end of this lesson, you will be able to:

• Understand what a pie chart is and its purpose
• Calculate angles for pie chart sections from frequency data
• Construct a simple pie chart using a protractor
• Read and interpret information from pie charts

Review: Frequency Tables

Yesterday we learned to organize data in tables:

What is a Pie Chart?

A pie chart is a circular graph divided into slices

Why called "pie chart"?
It looks like a pie or cake cut into pieces!

Each slice represents:

• One category from our data
• The size shows how big that category is
• Bigger slices = more items
• Smaller slices = fewer items

Why Use Pie Charts?

Advantages of pie charts:

• Easy to see which category is biggest/smallest
• Shows how the whole is divided into parts
• Visual and attractive
• Quick to understand at a glance

Example: Which travel method is most common?
With a pie chart, you can see immediately!

Understanding Circles and Angles

Key facts about circles:

• A complete circle = 360 degrees
• All slices together = 360°
• Each slice takes part of the 360°

This is why we need to calculate angles!

The Pie Chart Formula

To find the angle for each slice:

Angle = (Frequency ÷ Total) × 360°

What it means:

• Find what fraction the category is
• Multiply by 360° to get the angle
• This tells us how big to draw the slice

Example 1: Calculating Angles

Walking: 15 out of 35 learners

Four-step problem solving:

Understand: What fraction is 15 out of 35?
Plan: Use the formula
Work: (15 ÷ 35) × 360° = 0.43 × 360° ≈ 154°
Answer: Walking slice = 154°

Practice Together: More Angles

Let's calculate the remaining angles:

Bicycle: (5 ÷ 35) × 360° = 51°
Boda-boda: (10 ÷ 35) × 360° = 103°
Car/taxi: (5 ÷ 35) × 360° = 51°

Check: 154° + 51° + 103° + 51° = 359°
(Close to 360° - small difference due to rounding)

Drawing a Pie Chart: Materials

What you need:

• Paper and pencil
• Protractor (to measure angles)
• Compass or circular object (plate, lid, cup)
• Ruler
• Colored pencils (optional)

Make sure you have your protractor ready!

Step 1: Draw the Circle

Drawing your circle:

• Use a compass OR
• Trace around a circular object
• Make it big enough (about 10-12 cm diameter)
• Draw in your exercise book

Mark the center point clearly!

Step 2: Draw the Starting Line

Creating your starting point:

• Use your ruler
• Draw a line from center straight up (12 o'clock)
• This is your reference line
• All angles are measured from here

This line is like the first cut in a pie!

Step 3: Using the Protractor

How to measure angles with a protractor:

1. Place center of protractor on center of circle
2. Line up 0° mark with your starting line
3. Find the angle you need (e.g., 154°)
4. Make a small mark at that point
5. Draw a line from center through that mark

Step 4: Continue with Each Slice

For each category:

• Start from the PREVIOUS line (not the original line)
• Measure the next angle
• Draw the line
• Keep going until the circle is complete

The last slice should end exactly where you started!

Step 5: Label Each Slice

Make your chart clear:

• Write the category name in each slice
• Include the frequency number
• Example: "Walking (15)" or "Bicycle (5)"
• Add a title at the top

A chart without labels is useless!

Optional: Add Color

Making your pie chart attractive:

• Color each slice differently
• Use colored pencils or crayons
• Choose colors that contrast well
• This makes the chart easier to read

Remember: Charts must also work in black and white!

Reading a Pie Chart

What can we see from our chart?

• Which slice is biggest? (Walking)
• Which slices are equal? (Bicycle and Car/taxi)
• About what fraction is Boda-boda? (about 1/4)
• Most common travel method? (Walking)

Pie charts make comparisons visual!

Pie Charts vs. Tables

Comparing the two:

Both are useful - choose based on your needs!

Practice: Calculate These Angles

Favorite fruits in a class of 20:

• Mangoes: 6 learners
• Oranges: 9 learners
• Bananas: 3 learners
• Pineapples: 2 learners

Calculate the angle for Mangoes and Oranges

Answers: Fruit Angles

Mangoes:
(6 ÷ 20) × 360° = 0.3 × 360° = 108°

Oranges:
(9 ÷ 20) × 360° = 0.45 × 360° = 162°

Check your working!

When to Use Pie Charts

Pie charts work best when:

• Showing parts of a whole
• Comparing proportions
• Data has 3-7 categories (not too many!)
• You want visual impact
• Precise numbers aren't critical

Examples: Budget breakdown, market share, survey results

Common Pie Chart Mistakes

Avoid these errors:

• Forgetting to label slices
• Angles don't add up to 360°
• Reading protractor incorrectly
• Making circle too small
• Not checking calculations

Take your time and work carefully! ✓

Real-Life Pie Charts

Where do we see pie charts?

• News reports (election results, surveys)
• Business reports (sales by region, expenses)
• School reports (grade distributions)
• Weather data (types of weather days)

They're everywhere once you start looking!

Summary: Key Points

Today we learned:

• Pie charts show data as slices of a circle
• Use the formula: (Frequency ÷ Total) × 360°
• All angles must add to approximately 360°
• Draw carefully with protractor and ruler
• Label every slice clearly
• Pie charts show proportions visually

Looking Ahead

Tomorrow's lesson:
We will learn about line graphs to show how data changes over time

What to bring:

• Your exercise book
• Ruler and protractor
• Pencil and eraser

Homework

Assignment:

1. Use your homework data from Lesson 1 (about your family or home)
2. Calculate the angle for each category using the formula
3. Check that all angles add to approximately 360°
4. Draw a complete pie chart with:
   • Proper circle with center marked
   • Accurate angles measured with protractor
   • All slices labeled clearly
   • A title for your chart
5. Write two sentences about what your pie chart shows

Expected time: 25-30 minutes