Discussion

A wooden cylinder to be carved is 12 cm long and has a diameter of 45 mm. Taking \( \pi = 3.142 \), its total surface area is

Answer: C

Convert the diameter to centimetres first, then halve it.

\[ 45 \text{ mm} = 4.5 \text{ cm} \quad\Longrightarrow\quad r = 2.25 \text{ cm} \]

\[ \text{TSA} = 2\pi r (r + h) = 2 \times 3.142 \times 2.25 \times (2.25 + 12) \]

\[ = 14.139 \times 14.25 = 201.5 \approx 201 \text{ cm}^{2} \]

Both flat ends count, since the whole cylinder is carved; the curved surface alone would come to about 169.7 cm².

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