Mensuration (NCERT Ch. 10)

• Find the perimeter of regular and irregular closed figures.
• Find the perimeter of a rectangle and square.
• Find the area of a rectangle and square using a squared grid, then using formulas.

1. Perimeter = the total length of the boundary of a closed figure.
2. Perimeter of a rectangle = 2 × (length + breadth).
3. Perimeter of a square = 4 × side.
4. Area = the amount of surface enclosed by a closed figure, measured in square units.
5. Area of a rectangle = length × breadth.
6. Area of a square = side × side.

Find the perimeter and area of a rectangle with length 8 cm and breadth 5 cm.

Perimeter = 2 x (8 + 5) = 2 x 13 = 26 cm
Area = 8 x 5 = 40 sq cm

• Confusing perimeter (boundary, linear units) with area (surface, square units).
• Forgetting to multiply by 2 when finding rectangle perimeter.
• Using different units for length and breadth without converting first.

• Find the perimeter of a square of side 6 cm.
• Find the area of a rectangle 10 m by 4 m.

Open the Practice tab for graded questions on Mensuration (NCERT Ch. 10).