Two goods train each 500 m long, arc running in opposite directions on parallel tracks. Their speeds are 45 km /hr and 30 km/hr respectively Find the time taken by the slower train to pass the driver of the faster one.

A.  12 sec   
B.  24 sec
C.  48 sec   
D.  60 sec
Answer: C

Explanation:

Relative speed    = (45 + 30 )km/hr
                          = (75 x 5/18)m/sec
                          = (125 / 6) m/sec
Total Distance covered    = (500 + 500) m
                                      = 1000 m
Required time    = (1000 x 6 /125)sec
                         = 48 sec