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Subject – Mathematics

Chapter 9 – PERIMETER & AREA

Sub-topic 1 : PERIMETER AND IT’S UNIT

Perimeter: The length of the boundary of a closed figure is called the perimeter of the plane figure.
The units of perimeter are same as that of length, i.e., m, cm, mm, etc.

The perimeter of a two-dimensional shape is the distance around the shape. You can think of
wrapping a string around a triangle. The length of this string would be the perimeter of the triangle.
Or walking around the outside of a park, you walk the distance of the park’s perimeter. Some
people find it useful to think “perimeter” because the edge of an object is its rim and perimeter has
the word “rim” in it.

If the shape is a polygon, then you can add up all the lengths of the sides to find the perimeter.
Be careful to make sure that all the lengths are measured in the same units. You measure
perimeter in linear units, which is one dimensional. Examples of units of measure for length are
inches, centimeters, or feet

A grid is made of a number of unit squares. Figures are drawn on a grid.
The perimeter of a figure is the total length of its outline or boundary and this is found by counting
the number of unit lengths along the boundary of the figure.

Example: Find the perimeter of the shaded shape on the grid.

Solution

Step 1:

The shaded shape on the grid is a rectangle. Its length is 4 units and width is 3 units.
Step 2:

Perimeter of the shaded shape = 3 + 4 + 3 + 4 = 14 units