Quick Concept Summary
Mensuration becomes manageable when you first identify whether the question asks for boundary, surface, or capacity: perimeter, area, surface area, or volume.
Formula Table
| Figure | Formula |
|---|---|
| Rectangle | Area = l x b |
| Triangle | Area = 1/2 x b x h |
| Circle | Area = pi r^2 |
| Cube | Volume = a^3 |
| Cylinder | Volume = pi r^2 h |
Worked Examples
Example 1
A rectangle is 12 m x 8 m.
Area = 12 x 8 = 96 square m
Example 2
A cylinder has radius 7 cm and height 10 cm.
Volume = 22/7 x 7 x 7 x 10 = 1540 cubic cm
Practice Questions
1. Find the area of a circle of radius 14 cm. 2. Find the volume of a cube of side 6 cm. 3. A room is 10 m long and 8 m broad. Find flooring cost at Rs. 45 per square metre.
Common Mistakes
- Using diameter where radius is needed
- Ignoring square and cubic units
- Applying area formulas to perimeter questions