A train travels 250 km in 2 hours and 350 km in 4 hours.find the average speed of train. Choose the correct choice from the following answers
A) 80 kmph  B) 60 kmph  C) 70 kmph  D) 100 kmph  E) none of these

Rationale: "as we know that speed = distance / time for average speed = total distance / total time taken thus , total distance = 250 + 350 = 600 km thus , total speed = 6 hrs or , average speed = 600 / 6 or , 100 kmph . answer : d"
Answer: D