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STATEMENT - 1: The slant height of a cone's frustum is $4 cm$ and the circumferences of its circular ends are $18 cm$ and $6 cm$ respectively. The curved surface area is then $48 s q c m$ .
STATEMENT - 2: Frustum curved surface area $= π (r_{1} + r_{2})$ where $r_{1}$ and $r_{2}$ are frustum radii and l is a slant height.

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Statement 1 is False, Statement -2 is True

Statement -1 is True, Statement -2 is True: Statement 2 is NOT a correct explanation for Statement - 1

Statement -1 is True, Statement -2 is False

Statement -1 is True, Statement -2 is True, Statement - 2 is a correct explanation for Statement - 1

answer is C.

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Detailed Solution

Curved surface area of a frustum of a cone $= π (r_{1} + r_{2}) l$ , where $r_{1}$

and $r_{2}$ are radii of frustum and $l$ is a slant height.

Therefore Statement 2 is false.

Now for Statement 1 let us substitute the values in the CSA formula

$= \frac{22}{7} (\frac{9}{π} + \frac{3}{π}) \times 4$

$= \frac{22}{7 \times π} (9 + 3) \times 4$

$= \frac{22}{7} \times \frac{7}{22} (12) \times 4 = 48 {cm}^{2}$

Therefore Statement 1 is True.

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