Correct Answer - Option 3 :
50 sec
CALCULATION:
1st bike and train are travelling in opposite direction
⇒ Relative speed = 60 + 30 = 90 kmph = 25 m/sec
⇒ Length of train = 25 × 20 = 500 m
2nd bike and train are travelling in same direction
⇒ Relative speed = 60 - 24 = 36 kmph = 10 m/sec
⇒ Time taken = 500/10 = 50 sec
We will consider the length of the bike as negligible, as it is very small as compared to the length of the train.