उत्तर : 2. "2 : 1"
व्याख्या :

Answer: B) 2 : 1 Explanation: Given that train K crosses a pole in 30 seconds and train L crosses the same pole in one minute and 15 seconds. Let the length of train K be Lk and that of train L be Ll given that Lk = 3/4 Ll As the train K and L crosses the pole in 30 seconds and 80 seconds respectively, => Speed of train K = sk = Lk/30 Speed of train L = sl = Ll/80 Lk = 3/4 Ll => sk = 3/4 Ll/(30) = Ll/40 Ratio of their speeds = sk : sl = Ll/40 : Ll/80 => 1/40 : 1/80  =  2 : 1