Question
Find the radius of sphere whose surface area is $154 \mathrm{~cm}^2$.
✓
Answer
Let the radius of the sphere be rcm .
Surface area $=154 \mathrm{~cm}^2$
$\Rightarrow 4 \pi r^2=154$
$\Rightarrow 4 \times \frac{22}{7} \times r^2=154$
$\Rightarrow r^2=\frac{154 \times 7}{4 \times 22}=\frac{49}{4}$
$\Rightarrow r=\sqrt{\frac{49}{4}}=\frac{7}{2}$
$\Rightarrow \mathrm{r}=3.5 \mathrm{~cm}$
$\therefore$ the radius of the sphere is $3.5 \ cm .$
Surface area $=154 \mathrm{~cm}^2$
$\Rightarrow 4 \pi r^2=154$
$\Rightarrow 4 \times \frac{22}{7} \times r^2=154$
$\Rightarrow r^2=\frac{154 \times 7}{4 \times 22}=\frac{49}{4}$
$\Rightarrow r=\sqrt{\frac{49}{4}}=\frac{7}{2}$
$\Rightarrow \mathrm{r}=3.5 \mathrm{~cm}$
$\therefore$ the radius of the sphere is $3.5 \ cm .$
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