A man can row a boat at 10 kmph in still water and the speed of the stream is 8 kmph. What is then time taken to row a distance of 90 km down the stream ?  Select.
A) 8 hrs  B) 5 hrs  C) 15 hrs  D) 15 hrs  E) 20 hrs

Rationale: speed in down stream = 10 + 8 = 18 time taken to cover 90 km down stream = 90 / 18 = 5 hrs . answer : b
Answer: B