NCERT Class 8 Maths Mensuration

11.1 Introduction
We have learnt that for a closed plane figure, the perimeter is the distance around its boundary and its area is the region covered by it. We found the area and perimeter of various plane figures such as triangles, rectangles, circles etc. We have also learnt to find the area of pathways or borders in rectangular shapes.

In this chapter, we will try to solve problems related to perimeter and area of other plane closed figures like quadrilaterals.

We will also learn about surface area and volume of solids such as cube, cuboid and cylinder.

11.2 Let us Recall
Let us take an example to review our previous knowledge. This is a figure of a rectangular park (Fig 11.1) whose length is 30 m and width is 20 m.

(i) What is the total length of the fence surrounding it? To find the length of the fence we need to find the perimeter of this park, which is 100 m. (Check it)
(ii) How much land is occupied by the park? To find the land occupied by this park we need to find the area of this park which is 600 square meters (m2) (How?).
(iii) There is a path of one metre width running inside along the perimeter of the park that has to be cemented. If 1 bag of cement is required to cement 4 m2 area, how many bags of cement would be required to construct the cemented path?

We can say that the number of cement bags used = area of the path/area cemented by 1 bag
.
Area of cemented path = Area of park – Area of park not cemented.

Path is 1 m wide, so the rectangular area not cemented is (30 – 2) × (20 – 2) m2. That is 28 × 18 m2.

Hence number of cement bags used = ------------------

(iv) There are two rectangular flower beds of size 1.5 m × 2 m each in the park as shown in the diagram (Fig 11.1) and the rest has grass on it. Find the area covered by grass.

Please refer to attached file for NCERT Class 8 Maths Mensuration