KöMaL 2008 K165

Billy and Sophie are making rings out of paper strips and link them together to form chains. Each of them uses a 21×30 cm sheet of paper for making the chain. Billy cuts up the sheet parallel to the 21-cm sides, and a Sophie cuts it parallel to the 30-cm sides. Both of them make strips 1 cm wide, curve them into rings and glue them with 0-cm overlaps. The rings link together to form a chain without any deformation. Which chain is longer? (In calculating the perimeter of a circle, use 3.14 for the value of $\pi$, and disregard the thickness of the paper.)