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If two solid hemispheres of same base radius are joined together along their bases, then curved surface area of this new solid is

  • A.3πr²
  • B.4πr²
  • C.5πr²
  • D.6πr²

Answer: B

Two hemispheres joined along their flat faces make a complete sphere, and the two flat faces vanish inside it.

\[ \text{curved surface} = 2 \times 2\pi r^{2} = 4\pi r^{2} \]

which is exactly the surface area of a sphere of radius \( r \). The \( 3\pi r^{2} \) option is the total surface of a single solid hemisphere, base included - but that base is no longer exposed once the two are joined.

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