For Grade 5 Students (Ages 10-11) - Let's learn to measure the boundary of shapes!
In this lesson, you will learn to:
Hello, young mathematicians! In our previous lesson, we learned about different shapes. Today, we're going to learn about **perimeter**.
Imagine you have a garden and you want to put a fence around it. The length of that fence would be the **perimeter** of your garden!
The **perimeter** of a shape is the total distance around its outside edge. To find the perimeter, we add up the lengths of all its sides.
A square has four equal sides. So, to find its perimeter, you can add all four sides, or simply multiply the length of one side by $4$.
Formula: Perimeter of a Square = $4 \times \text{side}$
Example 1: Find the perimeter of a square with a side of $5$ cm.
Perimeter = $5$ cm + $5$ cm + $5$ cm + $5$ cm = $20$ cm
OR
Perimeter = $4 \times 5$ cm = $20$ cm
Exercise 1: Find the perimeter of the following squares.
Side = $7$ cm. Perimeter = $\underline{\hspace{2cm}}$ cm
Side = $12$ m. Perimeter = $\underline{\hspace{2cm}}$ m
A rectangle has four sides, but opposite sides are equal in length. It has a **length** and a **width**. To find its perimeter, you add up all four sides, or use the formula: $2 \times (\text{length} + \text{width})$.
Formula: Perimeter of a Rectangle = $2 \times (\text{length} + \text{width})$
Example 2: Find the perimeter of a rectangle with length $8$ cm and width $3$ cm.
Perimeter = $8$ cm + $3$ cm + $8$ cm + $3$ cm = $22$ cm
OR
Perimeter = $2 \times (8 + 3)$ cm = $2 \times 11$ cm = $22$ cm
Exercise 2: Find the perimeter of the following rectangles.
Length = $10$ cm, Width = $4$ cm. Perimeter = $\underline{\hspace{2cm}}$ cm
Length = $15$ m, Width = $5$ m. Perimeter = $\underline{\hspace{2cm}}$ m
Let's apply what we've learned to solve some real-life problems involving perimeter.
Exercise 3: Solve the following word problems.
A square playground has a side length of $20$ meters. What is the perimeter of the playground?
A rectangular table has a length of $120$ cm and a width of $60$ cm. What is the perimeter of the table?
A farmer wants to fence a rectangular field that is $50$ meters long and $30$ meters wide. How much fencing material does he need?
Let's check your answers!
Exercise 1: Perimeter of Squares
Exercise 2: Perimeter of Rectangles
Exercise 3: Problem Solving with Perimeter
Excellent work, Math Lanka students! You've learned about perimeter and how to calculate it for squares and rectangles. This is a very practical skill for many real-life situations!
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