only a single rail track exists between stations a and b on a railway line . one hour after the north bound super fast train n leaves station a for station b , a south - bound passenger train s reaches station a from station b . the speed of the super fast train is twice that of a normal express train e , while the speed of a passenger train s is half that of e . on a particular day , n leaves for b from a , 20 min behind the normal schedule . in order to maintain the schedule , both n and s increased their speeds . if the super fast train doubles its speed , what should be the ratio ( approximately ) of the speeds of passenger train to that of the super fast train so that the passenger train s reaches exactly at the scheduled time at a on that day ?