Correct Answer - Option 4 : 871 kms
Given:
Speed of goods train whose length is 1680 m and starts at 7 am = 48 km/hr
Speed of mail train whose length is 5320 m and starts at 12 noon = 67 km/hr
Concept used:
Relative speed when direction is same = Difference of both speeds
Distance = Speed × Time
Calculation:
Relative speed = (67 – 48) km/hr
⇒ 19 km/hr
Distance covered by goods train between 7 am to 12 noon (5 hours) = (48 × 5) km
⇒ 240 km
So, Total distance = 240 km + 1680 m + 5320 m
⇒ 240 km + 7 km = 247 km
Time taken by mail train to cross goods train = 247/19
⇒ 13 hours
Distance covered by mail train in 13 hours = (13 × 67) km
⇒ 871 km
∴ The required distance is 871 km