A trained covered x km at 50 kmph and another 2x km at 20 kmph. Find the average speed of the train in covering the entire 3x km.
Choose the correct choice from the following:
A) 22
B) 99
C) 25
D) 66
E) 887

Rationale: "total time taken = x / 50 + 2 x / 20 hours = 6 x / 50 = 3 x / 25 hours average speed = 3 x / ( 3 x / 25 ) = 25 kmph answer : c"
Answer: C