Page 129 - ICSE Math 4

P
10 Perimeter and Areaerimeter and Area

Learning Outcomes

Students will be able to learn:
 to find the perimeter of plane figures using their side lengths and square grid.
 to find the area of plane figures using their side lengths.
 to find the area of regular and irregular plane figures by counting squares .

We have already learnt about basic shapes. Now let’s learn how to fi nd the perimeter and
area of some basic shapes.

Perimeter

Mr Verma wants to fence his garden to protect it from

animals.
To fi nd out how much wire he needs for fencing, he
takes a long rope and es a knot at one of its end. Then
he starts moving from one corner of the garden along
its boundary to the next corner. He es a knot in the

rope at this par cular point. Then he moves further
and es a knot at every corner that he reaches.
When he reaches the corner from where he had started, he es the last knot. The rope

looks as shown:

He now measures the rope from the fi rst knot to the last knot and fi nds it to be 20 m long.

5 m 5 m 5 m 5 m

This length of rope that is used to measure the boundary around the garden is its perimeter.
A ruler or a measuring tape can also be used to measure the boundary or perimeter of the
objects.

Thus, perimeter is the total length of the boundary of a plane closed fi gure. The word
perimeter is derived from the Greek word “Peri” meaning “around” and “meter” meaning
“measure”. In short, perimeter means the total or sum of all the sides of a given plane
closed fi gure.

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