Question

A rectangular paper is folded into a cylinder. The length and breadth of the paper are L and B respectively. The surface area of the cylinder is

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Answer 1

The cylinder is a 3-D object. Here the 3-D surface of the cylinder can be unrolled into a 2-D rectangular sheet of paper. The area of the 3-D surface and that of the 2-D plane are the same. It is clear that the area of rectangle = Length $\times$ Breadth= LB