Discussion

The surface area of a sphere is 616 cm². Its radius is

Answer: A

Solve the surface-area formula for \( r \), taking \( \pi = \tfrac{22}{7} \).

\[ 4\pi r^{2} = 616 \]

\[ r^{2} = \frac{616 \times 7}{4 \times 22} = \frac{4312}{88} = 49 \]

\[ r = 7 \text{ cm} \]

Using \( 2\pi r^{2} \) - the hemisphere formula - would give \( r = 7\sqrt{2} \approx 9.9 \) cm instead.

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