Discussion
The volume of a right circular cylinder of length 1·2 metres is 4620 cm3. What is the curved surface area (in cm2) of the cylinder ? (Take \(\pi = \dfrac{22}{7}\))
Answer: A
The curved surface area is 2640 square cm.
The length is 1.2 m = 120 cm. From the volume:
\[ \begin{aligned} \frac{22}{7} r^{2} \times 120 &= 4620 \\ r^{2} &= \frac{4620 \times 7}{22 \times 120} = 12{\cdot}25 \\ r &= 3{\cdot}5\ \text{cm} \\ \text{CSA} &= 2 \times \frac{22}{7} \times 3{\cdot}5 \times 120 = 2640 \end{aligned} \]
The common error is to leave the length as 1.2 or 12 instead of converting it to 120 cm, which gives a wrong radius; the other options do not follow from a radius of 3.5 cm.
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