Bunuel wrote:
Between a cube and a right circular cylinder, does the cube have a higher lateral surface area? Lateral surface area refers to the area of the sides (the two base areas, one on top and one on bottom, are not taken into account). Assume π = (3/2)^3
(1) The height of the cylinder is twice its radius.
(2) Both the cube and the cylinder have the same volume.
Call the side of the cube is \(a\), the volume of the cube is \(a^3\) and the lateral surface area of the cube is \(4a^2\)
Call the height and the radius of the cylinder are \(h\) and \(b\). The volume of the cylinder is \(\pi hb^2\) and the lateral surface area of the cylinder is \(2\pi bh\)
(1) Since we could know \(h=2b\), however we can't know the value of \(a\). Insufficient.
(2) We have \(a^3 = \pi hb^2\). We have to compare \(4a^2\) and \(2\pi bh\)
Since \(a^3 = \pi hb^2 \implies 2 \pi bh = \frac{2a^3}{b}\) . We now have to compare \(\frac{2a^3}{b}\) and \(4a^2\) or we have to compare \(\frac{a}{b}\) and 2. However, we have no information about \(\frac{a}{b}\), insufficient.
Combine (1) and (2):
From (1) have \(h=2b\).
From (2) have \(a^3 = \pi hb^2 = 2\pi b^3 \implies \frac{a}{b} = \sqrt[3]{2\pi}\)
Now, from given condition we have \(\pi = (\frac{3}{2})^3 \\
\implies 2\pi = 2 * \frac{27}{8} = \frac{27}{4} < 8 \\
\implies \sqrt[3]{2\pi} < 2 \)
From this, we could compare \(\frac{a}{b}\) and 2 or we could compare \(\frac{2a^3}{b}\) and \(4a^2\). Sufficient.
The answer is C