The poster you are giving your friend is in a cardboard tube with a 2 in diameter and 26 in length. will a rectangular piece of wrapping paper that is 8 in by 28in completely cover the tube

I am pretty positive that it would, the circumference of the tube comes out to roughly 6.28 inches, so thee 8 inch wrapping paper should cover it nicely. Now the sheet of paper is only 2 inches longer than the tube, so the paper will only extend one inch above the tubes edge on either end. the tube has a diameter of 2 inches, so the 1 inch extension all around the tube should fold in and match up quite nicely. 

11/2.2 = 5 inches for the length 8.5/2.2= 3.86 inches for the width