How many seconds will a 620 metre long train take to cross a man running with a speed of 8 km/hr in the direction of the moving train if the speed of the train is 80 km/hr?
Choose the correct choice from the following answers.
A) 25  B) 30  C) 31  D) 45  E) 60

Rationale: "explanation : speed of train relatively to man = ( 80 - 8 ) km / hr = 72 km / hr = ( 72 x 5 / 18 ) m / sec = 20 m / sec time taken to pass the man = ( 620 / 20 ) sec = 31 sec . answer : c"
Answer: C