Grade 3
  1. Number Sense and Numeration  1.1. Understanding Numbers  1.1.1. Reading and Writing Numbers up to 10,000  1.1.2. Place Value up to Thousands  1.1.3. Comparing and Ordering Numbers  1.1.4. Rounding Numbers to the Nearest Ten and Hundred  1.1.5. Skip Counting by 2s, 5s, 10s, and 100s up to 1,000  1.2. Operations with Whole Numbers  1.2.1. Addition and Subtraction up to 1,000  1.2.2. Multiplication Facts (up to 10 x 10)  1.2.3. Division Facts (up to 100)  1.2.4. Multiplication as Repeated Addition  1.2.5. Division as Equal Sharing  1.2.6. Word Problems with Addition, Subtraction, Multiplication, and Division  1.3. Estimation  1.3.1. Estimating Sums and Differences  1.3.2. Estimating Products and Quotients  1.4. Understanding Even and Odd Numbers
  2. Fractions and Decimals  2.1. Understanding Fractions  2.1.1. Identifying and Representing Fractions  2.1.2. Fractions of a Whole and Part of a Set  2.1.3. Comparing and Ordering Fractions with Like Denominators  2.1.4. Equivalent Fractions  2.1.5. Simple Fraction Word Problems  2.2. Introduction to Decimals  2.2.1. Tenths and Hundredths as Decimals  2.2.2. Relationship between Fractions and Decimals
  3. Measurement  3.1. Length  3.1.1. Measuring in Centimeters and Meters  3.1.2. Comparing and Ordering Lengths  3.1.3. Estimating Lengths  3.1.4. Converting Between Centimeters and Meters  3.2. Mass  3.2.1. Measuring in Grams and Kilograms  3.2.2. Estimating and Comparing Mass  3.3. Capacity  3.3.1. Measuring in Milliliters and Liters  3.3.2. Estimating and Comparing Capacity  3.4. Time  3.4.1. Telling Time to the Nearest Minute  3.4.2. Calculating Elapsed Time  3.4.3. Using a Calendar  3.4.4. Understanding A.M. and P.M.  3.5. Area and Perimeter  3.5.1. Calculating Perimeter of Simple Shapes  3.5.2. Estimating and Measuring Area of Shapes  3.5.3. Finding Area by Counting Squares
  4. Geometry  4.1. Properties of Shapes  4.1.1. Identifying 2D Shapes (Triangles, Quadrilaterals, Circles, etc.)  4.1.2. Identifying 3D Shapes (Cubes, Spheres, Cylinders, etc.)  4.1.3. Describing Attributes of 2D and 3D Shapes  4.1.4. Recognizing Parallel and Perpendicular Lines  4.2. Symmetry and Transformations  4.2.1. Recognizing Lines of Symmetry  4.2.2. Identifying Flips, Slides, and Turns  4.3. Angles  4.3.1. Understanding Right Angles  4.3.2. Comparing Angles (Acute, Right, Obtuse)
  5. Data Management and Probability  5.1. Data Collection and Organization  5.1.1. Collecting Data using Surveys and Experiments  5.1.2. Organizing Data using Tally Charts and Tables  5.2.1. Creating and Interpreting Pictographs  5.2.2. Creating and Interpreting Bar Graphs  5.2.3. Reading Simple Line Graphs  5.3. Probability  5.3.1. Understanding Basic Probability Terms (Certain, Possible, Impossible)  5.3.2. Predicting Outcomes  5.3.3. Simple Probability Experiments
  6. Patterns and Algebra  6.1. Patterns  6.1.1. Identifying and Extending Numeric Patterns  6.1.2. Identifying and Extending Shape Patterns  6.1.3. Creating Patterns Using Rules  6.2. Introduction to Algebra  6.2.1. Understanding Variables as Unknowns  6.2.2. Solving Simple Addition and Subtraction Equations  6.2.3. Using Patterns to Solve Problems
  7. Problem-Solving Skills  7.1. Strategies for Problem-Solving  7.1.1. Using Pictures or Diagrams  7.1.2. Identifying Patterns in Problems  7.1.3. Making Organized Lists  7.1.4. Guessing and Checking  7.1.5. Using Logical Reasoning  7.1.6. Breaking Down Problems into Steps

Grade 3 → Measurement → Area and Perimeter ↓


Calculating Perimeter of Simple Shapes


Perimeter is a term used in geometry to describe the total length around a shape. When we calculate perimeter, we essentially add up all of the sides of a shape to determine how long the boundary of that shape is. This is a fundamental concept that lays the groundwork for understanding more complex mathematical ideas. Let's dive into the world of perimeter, focusing specifically on simple shapes like squares, rectangles, and triangles.

Understanding the perimeter

Before we calculate the perimeter, let's make sure we understand what the perimeter means. Imagine you have a small garden. The fence around your garden is the perimeter. If you need to buy materials to build a new fence, you need to know how tall the fence should be, which means knowing the perimeter.

Perimeter of a square

A square is a shape that has four equal sides. To find the perimeter of a square, you can add the lengths of the four sides.

Perimeter of a square = side + side + side + side
or only,
Perimeter = 4 × side
Side

For example, if each side of a square is 5 units long, the perimeter is:

Perimeter = 4 × 5 = 20 units

Therefore, the fence around the square should be 20 units long.

Perimeter of a rectangle

A rectangle is a shape whose opposite sides are equal. It has two lengths and two widths. To find the perimeter, we add the length and width together. Here's the formula:

Perimeter of rectangle = 2 × (length + breadth)
LengthWidth

If the length of a rectangle is 8 units and width is 3 units, then:

Perimeter = 2 × (8 + 3) = 2 × 11 = 22 units

This means that the perimeter of the rectangle is 22 units.

Perimeter of a triangle

A triangle has three sides, and the perimeter is the sum of all its sides. Here's how you can calculate it:

Perimeter of triangle = side1 + side2 + side3
Side 1Side 2Side 3

For example, if the sides of a triangle are 6, 7, and 8 units, then the perimeter is:

Perimeter = 6 + 7 + 8 = 21 units

The perimeter of this triangle is 21 units.

Calculating perimeter with different units

Sometimes, the units we use to measure may change depending on the scenario. Whether it is centimeters, meters or inches, the way to calculate the perimeter remains the same, but we note the units properly. For example, a garden fence may be measured in meters, while the perimeter of a book may be calculated in centimeters.

Example

Consider a rectangle whose length is 4 m and width is 2 m. The perimeter will be:

Perimeter = 2 × (4 + 2) = 2 × 6 = 12 m

For a notebook 10 inches in length and 8 inches in width, the perimeter would be:

Perimeter = 2 × (10 + 8) = 2 × 18 = 36 inches

Practical applications of perimeter

Understanding how to calculate perimeter is useful in many real-world situations. Whether you're sewing a border around a piece of fabric, installing new flooring in a rectangular room, or putting up a fence around your yard, calculating the perimeter lets you know how much material you'll need.

Another example: planning a small playground

Imagine you are planning to build a small rectangular playground. You want to fence it around so that children can play safely. If the playground is 20 m long and 15 m wide, how much fencing material will you need?

Perimeter = 2 × (length + breadth)
Perimeter = 2 × (20 + 15) = 2 × 35 = 70 m

This shows that we need 70 meters of fencing material.

More complex shapes

While we've focused on simple shapes, sometimes you'll come across more complex shapes. For these, the basic idea remains: add the lengths of all the sides together. For example, if you have an L-shaped garden, find the perimeter by breaking it up into parts that you can measure as rectangles.

Example of an L-shape perimeter

For an L-shaped plot, you can think of it as two rectangles joined together. You find the perimeter by calculating each part separately and then adding them together, making sure each side is counted only once.

Let's review

  • The perimeter is the total distance around the edge of a shape.
  • For a square, multiply the length of one side by four.
  • For a rectangle, add the length and width and multiply by two.
  • For a triangle, add up the three sides.

Understanding how to calculate perimeter can be incredibly useful in everyday life. From planning rooms, decorating spaces or even determining how much paint you need to buy, it all depends on understanding the boundaries of the space you're working in. With practice, calculating perimeter becomes an easy and intuitive task.

Practice problems

  1. Find the perimeter of a square with side 9 units.
  2. The length of a rectangle is 15 units and width is 5 units, what is its perimeter?
  3. Find the perimeter of a triangle with sides 7 units, 10 units and 5 units.

Work on these to strengthen your understanding of perimeter calculations. Practice consistently, and you'll find that you'll master this concept in no time.


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Calculating Perimeter of Simple Shapes

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