Question:
If four times the sum of the areas of two circular faces of a cylinder of height 8 cm is equal to twice the curve surface area, then diameter of the cylinder is
(a) 4 cm
(b) 8 cm
(c) 2 cm
(d) 6 cm
Solution:
Let r be the radius of cylinder.
Area of circular base of cylinder 
The height of cylinder h = 8 cm
The C.S.A. of cylinder
Clearly,
$4 \times\left(\pi r^{2}+\pi r^{2}\right)=2 \times(\pi r)$
The diameter of cylinder
Hence, the correct answer is choice (b).
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