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Points to Remember: Mensuration | Mathematics (Maths) Class 8 PDF Download

Important Formulae

1. Area of a parallelogram = Base * Height

Points to Remember: Mensuration | Mathematics (Maths) Class 8

2. Area of a triangle = 1/2 * Base * Height

3. Area of a trapezium = 1/2 * [Sum of parallel sides] * Height

4. Area of a rhombus = 1/2 * Product of diagonals

Points to Remember: Mensuration | Mathematics (Maths) Class 8

5. Surface area of

(i) a cuboid = 2[lb + bh + hl]

Points to Remember: Mensuration | Mathematics (Maths) Class 8

(ii) a cube = 6a2

Points to Remember: Mensuration | Mathematics (Maths) Class 8

(iii) a cylinder = 2πr(r + h)

Points to Remember: Mensuration | Mathematics (Maths) Class 8

6. Volume of

(i) cuboid = l * b * h

Points to Remember: Mensuration | Mathematics (Maths) Class 8

(ii) cube = l3

Points to Remember: Mensuration | Mathematics (Maths) Class 8

(iii) cylinder = πr2h

Points to Remember: Mensuration | Mathematics (Maths) Class 8

  • 1 m3 = 1000 litres
  • A square, a rectangle, a trapezium, a rhombus, a parallelogram, a triangle, a circle, etc., are plane figures and the surfaces enclosed by their boundaries are called areas. We have formulae to find their areas. The perimeter is the distance around a figure. The plane figures are also called 2-D shapes. The solids such as cubes, cuboids, cylinders are called 3-D shapes. A 3-D shape is bounded by faces. These faces can be rectilinear or curved or both. 
  • We also know that:
    (i) The area of a square = Side * Side
    (ii) The area of a rectangle = Length * Breadth
    (iii) The area of a circle = πr2 [where r is the radius]
    (iv) The area of triangle = 1/2 * Base * Altitude
    (v) The area of a parallelogram = Base * Height

Note: 
I. All angles of a regular polygon have equal degree measures.
II. All sides of a regular polygon are equal in length.

Solved Examples

Q1. The length and breadth of a rectangle are 10 cm and 8 cm respectively. Find its perimeter if the length and breadth are (i) doubled (ii) halved..
Ans: 

Length of the rectangle = 10 cm
Breadth of the rectangle = 8 cm
(i) When they are doubled,
l = 10 × 2 = 20 cm
and b = 8 × 2 = 16 cm
Perimeter = 2(l + b) = 2(20 + 16) = 2 × 36 = 72 cm
(ii) When they are halved,
l = 10/2 = 5 cm
b = 8/2 = 4 cm
Perimeter = 2(l + b) = 2(5 + 4) = 2 × 9 = 18 cm

Question for Points to Remember: Mensuration
Try yourself:Q2. If the lateral surface of the cylinder is 500 cm² and its height is 10 cm, then find the radius of its base.
View Solution

Q2. A horse is tethered by a rope 10 m long at a point. Find the area of the region where it can graze (π = 3.14)
Solution: 
The area of the region the horse can graze is circular with a radius equal to the length of the rope.
The area of the circle is given by πr²
= 3.14 × 10²
= 3.14 × 100
=314
Hence the area of the region the horse can graze is 314 cm².

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FAQs on Points to Remember: Mensuration - Mathematics (Maths) Class 8

1. What are the basic formulae for calculating the area and perimeter of common shapes in mensuration?
Ans.The basic formulae for calculating area and perimeter are as follows: - Rectangle: Area = Length × Breadth; Perimeter = 2(Length + Breadth) - Square: Area = Side × Side; Perimeter = 4 × Side - Triangle: Area = (Base × Height) / 2; Perimeter = Sum of all sides - Circle: Area = π × Radius²; Circumference (perimeter) = 2π × Radius.
2. How do you calculate the volume of 3D shapes like cubes and cylinders in mensuration?
Ans.The volume of common 3D shapes can be calculated using these formulas: - Cube: Volume = Side³ - Rectangular Prism: Volume = Length × Breadth × Height - Cylinder: Volume = π × Radius² × Height - Cone: Volume = (1/3) × π × Radius² × Height.
3. What is the difference between area and volume in mensuration?
Ans.Area measures the space inside a two-dimensional shape (like squares, rectangles, etc.) and is expressed in square units (e.g., cm², m²). Volume measures the space inside a three-dimensional object (like cubes, cylinders, etc.) and is expressed in cubic units (e.g., cm³, m³).
4. How can I apply mensuration formulas in real-life situations?
Ans.Mensuration formulas are used in various real-life situations, such as: - Calculating the amount of paint needed for a wall (area). - Determining the volume of water a tank can hold (volume). - Estimating land area for agriculture or construction (area). - Designing packaging for products (volume of boxes).
5. Are there any tips for solving mensuration problems quickly and accurately?
Ans.Yes, here are some tips: - Familiarize yourself with the key formulas for different shapes. - Draw diagrams to visualize the problem whenever possible. - Break complex problems into smaller, manageable parts. - Practice regularly to improve speed and accuracy. - Double-check your calculations to avoid simple mistakes.
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