Question 19

Four times the area of the curved surface of a cylinder is equal to 6 times the sum of the areas of its bases. If its height is 12 cm then its curved surface area correct to two decimal places is (use $$\pi = \frac{22}{7}$$)

We have $$4 \times 2\pi r h = 6 \times 2\pi r^2$$, so $$4h = 6r$$ and $$r = \frac{4 \times 12}{6} = 8$$ cm. The curved surface area is $$2 \times \frac{22}{7} \times 8 \times 12 = \frac{4224}{7} \approx 603.43\ \text{cm}^2$$.

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