• # question_answer Two trains each of length 90m, run on parallel tracks. When running in the same direction, the faster train passes the slower train completely in 18 seconds, but when they are running in opposite directions at speeds same as before, they cross each other in 9 seconds. The speed of second train is A)  5 m/s B)         15 m/s C)  8 m/s   D)  6 m/s

[a] Let speed of first train = x km/h speed of second train = y km/h $\therefore$ In same direction$=18=\frac{90+90}{x-y}$ $x-y=10$                     ? (1) In opposite direction $=9=\frac{90+90}{x+y}$ $x+y=20$                    ... (2) By (1) and (2) x = 15, y = 5 $\therefore$ speed of second train = 5 km/h