A trained covered x km at 40 kmph and another 2x km at 20 kmph. Find the average speed of the train in covering the entire 4x km.	Choose the correct choice from the following answers.
A) 16 B) 18 C) 32 D) 19 E) 12

Rationale: "total time taken = x / 40 + 2 x / 20 hours = 5 x / 40 = x / 8 hours average speed = 4 x / ( x / 8 ) = 32 kmph answer : c"
Answer: C