Perimeter

In your book, Maths Mela (Chapter 6), Bhola is making a boundary of bricks around his vegetable garden. The boundary goes all the way round the edge of the garden. The length of the boundary of a shape is called its perimeter.

The book draws shapes on a dot grid where the dots are 1 cm apart. To find the perimeter, start at one corner and walk all the way round the edge, counting every 1 cm side until you are back where you started. Take a rectangle 4 cm long and 1 cm wide. Going round: 4 cm along the top, 1 cm down, 4 cm along the bottom, 1 cm up. 4 + 1 + 4 + 1 = 10, so its perimeter is 10 cm.

A square with 2 cm sides has four sides of 2 cm each: 2 + 2 + 2 + 2 = 8 cm. The book's worked example is an L shape: along the top 2 cm, down 1 cm, across 1 cm, down 1 cm, along the bottom 3 cm, and up 2 cm to the start. 2 + 1 + 1 + 1 + 3 + 2 = 10 cm. So the L shape and the 4 cm by 1 cm rectangle have the same perimeter, even though they look different!

Different shapes can have the same perimeter. A square with 5 cm sides has perimeter 5 + 5 + 5 + 5 = 20 cm. A rectangle 6 cm long and 4 cm wide also has perimeter 6 + 4 + 6 + 4 = 20 cm.