The time taken by a man to row his boat upstream is twice the time taken by him to row the same distance downstream. If the speed of the boat in still water is 18 kmph, find the speed of the stream?
Options:
A) 8 kmph  B) 9 kmph  C) 7 kmph  D) 6 kmph  E) 5 kmph

Rationale: "the ratio of the times taken is 2 : 1 . the ratio of the speed of the boat in still water to the speed of the stream = ( 2 + 1 ) / ( 2 - 1 ) = 3 / 1 = 3 : 1 speed of the stream = 18 / 3 = 6 kmph . answer : d"
Answer: D