get close close mathematician Serval university student math major Japari University on Calculus class teacher teach calculate expect length random subsegment give segment then leave bonus problem homework award garage kit IOI the bonus extend problem general case followsyou give segment length l we randomly choose n segment choose point maybe noninteg coordinate give segment equiprobably interval point form segment you give number random segment n integer k the 2n endpoint choose segment split segment 2n1 interval your task calculate expect total length interval cover k segment n random segmentsyou find answer modulo 998244353