Example 1 · level 1
Find the surface area of a football of radius 21 cm (in cm²). Use π = 22/7.
Show solution
- SA = 4 × 22/7 × 21² = 5,544 cm².
Answer: 5,544
CLASS 9 MATHS · SURFACE AREAS AND VOLUMES
Surface area and volume of cones and spheres
Cone: CSA = πrl, V = ⅓πr²h, l² = r² + h². Sphere: SA = 4πr², V = 4/3 πr³. Hemisphere: TSA = 3πr². Use π = 22/7.
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Worked examples
Example 2 · level 2
Find the volume of a cone with radius 21 cm and height 20 cm (in cm³). Use π = 22/7.
Show solution
- V = ⅓ × 22/7 × 441 × 20 = 9,240 cm³.
Answer: 9,240
Example 3 · level 3
Find the volume of a sphere of radius 14 cm (in cm³, to 2 decimal places if needed). Use π = 22/7.
Show solution
- V = 4/3 × 22/7 × 14³ = 4/3 × 22/7 × 2744
- = 11,498.6667 cm³.
Answer: 11,498.6667