How to find the surface area of a sphere - GRE Quantitative Reasoning

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Question

A sphere has a surface area of square inches. If the radius is doubled, what is the surface area of the larger sphere?

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Answer

The surface area of the larger sphere is NOT merely doubled from the smaller sphere, so we cannot double to find the answer.

We can use the surface area formula to find the radius of the original sphere.

_r_2 = 4

r = 2

Therefore the larger sphere has a radius of 2 * 2 = 4.

The new surface area is then square inches.

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