# Ex.13.4 Q8 Surface Areas and Volumes Solution - NCERT Maths Class 9

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## Question

A hemispherical bowl is made of steel, **\(0.25 \rm\,cm\)** thick. The inner radius of the bowl is \(5\rm\, cm.\) Find the outer curved surface area of the bowl.

## Text Solution

**Reasoning:**

The surface area of the hemisphere is half of the surface area of the sphere.

**What is known?**

Thickness of steel.

**What is unknown?**

Outer curved surface area.

**Steps:**

Inner radius bowl \(= 5\rm\, cm\)

Thickness of steel \(= 0.25\rm\, cm\)

Outer radius of the bowl

\(= 5+0.25\\=5.25 \rm{cm}\)

Curve Surface area of the hemisphere,

\[\begin{align}&= 2\pi {r^2} \\&= 2 \times \frac{{22}}{7} \times {(5.25)^2}\\&= 173.25\,\,\rm{cm^2} \end{align}\]

**Answer:**

The outer curved surface area of the hemisphere

\[\begin{align} = 173.25\,\rm{cm^2} \end{align}\]