Question

Find the surface area (in cm²) of a sphere whose diameter is 21 cm.

• A. 1346
• B. 1386
• C. 1286
• D. 1316

Answer 1

Answer:

B. 1386

Diameter = 21 cm

Step 1: Find radius

$r = \frac{21}{2} = 10.5 \text{ cm}$

Step 2: Formula for surface area of a sphere

$\text{Surface Area} = 4\pi r^2$

Step 3: Substitute the value

$= 4 \times \frac{22}{7} \times (10.5)^2$

$(10.5)^2 = 110.254$
$= 4 \times \frac{22}{7} \times 110.25$
$= 4 \times 22 \times 15.75$
$= 88 \times 15.75$
= 1386
Surface area = 1386 cm²