Course Content
Class 7th Science
0/36
Class 7th Math
0/71
Class 7 Social Science Geography
0/20
Class 7 Social Science History
0/20
Class 7 Social Science Civics
0/19
Class 7 English Honeycomb
0/20
Class 7 English Honeycomb Poem
0/18
Class 7 English An Alien Hand Supplementary
0/20
Online Class For 7th Standard Students (CBSE)

## Perimeter and Area Class 7 Notes: Chapter 11

### Perimeter

• Perimeter is the total length or total distance covered along the boundary of a closed shape ### Area

• The area is the total amount of surface enclosed by a closed figure. Areas of a closed figure

### The perimeter of Square and Rectangle

• Perimeter of a square = a + a + a + a = 4a, where a is the length of each side. • Perimeter of a rectangle = l + l + b + b = 2(l + b), where l and b are length and breadth, respectively. Rectangle with length ‘l’ units and breadth ‘b’ units  • Area of each triangle = 12 (Area of the rectangle).
=  12(10cm×5cm)
=  25cm2

### Area of a Triangle

• Consider a parallelogram ABCD.
• Draw a diagonal BD to divide the parallelogram into two congruent triangles. • Area of triangle ABD = 1/2 (Area of parallelogram ABCD)

Area of triangle ABD  = 1/2 (b×h)

### Conversion of Units

• Kilometres, metres, centimetres, millimetres are units of length.
• 10 millimetres = 1 centimetre
• 100 centimetres = 1 metre
• 1000 metres = 1 kilometre

### Terms Related to Circle

• circle is a simple closed curve which is not a polygon.
• A circle is a collection of points which are equidistant from a fixed point. • The fixed point in the middle is called the centre.
• The fixed distance is known as radius.
• The perimeter of a circle is also called as the circumference of the circle. ### Introduction and Value of Pi

• Pi (π)  is the constant which is defined as the ratio of a circle’s circumference (2πr) to its diameter(2r).

π= Circumference (2πr)/Diameter (2r)

• The value of pi is approximately equal to 3.14159 or 22/7.

## Problem Solving

### Cost of Framing, Fencing

• Cost of framing or fencing a land is calculated by finding its perimeter.
• Example: A square-shaped land has length of its side 10m.
Perimeter of the land = 4 × 10 = 40m
Cost of fencing 1m = Rs 10
Cost of fencing the land = 40 m × Rs 10 = Rs 400

### Cost of Painting, Laminating

• Cost of painting a surface depends on the area of the surface.
• Example: A wall has dimensions 5m×4m.
Area of the wall = 5m×4m=20m2
Cost of painting 1m2 of area is Rs 20.
Cost of painting the wall =20m2×Rs 20=Rs 400

### Area of Mixed Shapes

• Find the area of  the shaded portion using the given information. Solution: Diameter of the semicircle = 10cm