If the surface area of a sphere is cm2, then what is the radius of that sphere? [Use π = ]
- AOption (a)
14 cm
- BOption (b)
13 cm
- COption (c)
12 cm
- DOption (d)
11 cm
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Correct answer
13 cm
Why this answer is correct
Shortcut Trick
Surface Area = 4 × π × r2
r2 = (Total Surface Area) ÷ (4 × π)
r2 = (14872/7) × (1/4) × (7/22) = 14872 ÷ 88 = 169
r = √169 = 13 cm
∴ The correct answer is 13 cm.
Alternate Method
Given:
Surface Area (S) = cm2 = (2124 × 7 + 4) ÷ 7 = 14872 ÷ 7 cm2
π =
Formula Used:
Surface Area of Sphere = 4πr2
Calculations:
⇒ 4 × (22/7) × r2 = 14872/7
⇒ 88/7 × r2 = 14872/7
⇒ 88 × r2 = 14872
⇒ r2 = 14872 ÷ 88
⇒ r2 = 169
⇒ r = √169
⇒ r = 13 cm
∴ The correct answer is 13 cm.
Additional Information
Volume of a Sphere
The amount of space occupied by a sphere is given by V = (4/3)πr3.
Hemisphere Properties
Curved Surface Area = 2πr2 and Total Surface Area = 3πr2.
Ratio of Surface Area to Volume
For a sphere, the ratio of Surface Area (S) to Volume (V) is S/V = 3/r.


