Speed of two trains 'A' and 'B' is 12 m/s and ___ m/s respectively. Length of 'B' and 'A' is ___ metres and 240 metres, respectively. Time taken by the trains to cross each other when moving in same direction is 40 seconds. The data given in which among the given options will fill the blank in the same order so as to make the statement true?
I. 20, 80
II. 3, 120
III. 29, 440

Solution

Statement I: Relative speed = 20 - 12 = 8 m/s
Sum of length of both the trains = 80 + 240 = 320 metres
Time taken to cross each other = (320/8) = 40 seconds So, statement I is true. Statement II: Relative speed = 12 - 3 = 9 m/s
Sum of length of both the trains = 120 + 240 = 360 metres
Time taken to cross each other = (360/9) = 40 seconds So, statement II is true. Statement III: Relative speed = 29 - 12 = 17 m/s
Sum of length of both the trains = 440 + 240 = 680 metres
Time taken to cross each other = (680/17) = 40 seconds So, statement III is true. Therefore, all statements I, II and III are true. Hence, option A.