Question

A rectangular piece of paper measuring 25cm by 21cm is

rolled along its breadth to form a cylinder. Find the total
surface area of the cylinder so formed.

Answer 1

The surface area is the area of the rectangle - it has been rolled so no different.

25 x 21 = 525 cm^2

Answer 2

The area of the piece of paper is (25cm x 21cm) = 525 cm² .

There's no reason it should change when you bend the paper
into different shapes.