Example problem of a sphere — lesson. Mathematics CBSE, Class 9.

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The diameter of an orange is \(7 \ cm\). Find the surface area of \(50\) oranges.

Solution:

Diameter of an orange \((d)\) \(=\) \(7 \ cm\)

Radius of an orange \((r)\) \(=\)

\frac{d}{2} = \frac{7}{2} = 3.5 cm

Surface area of a sphere \(=\) \(4 \pi r^2\) sq. units

\(=\)

4 \times \frac{22}{7} \times {(3.5)}^{2}

\(=\)

4 \times \frac{22}{7} \times 12.25

\(=\) \(154\)

Surface area of an orange \(=\) \(154\) \(cm^2\).

Surface area of \(50\) oranges:

\(=\) \(154 \times 50\)

\(=\) \(7700\)

Therefore, the surface area of \(50\) oranges is \(7700 \ cm^2\).

Important!

The value of \(\pi\) should be taken as \(\frac{22}{7}\) unless its value is shared in the problem.

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3. Example problem of a sphere