A man rows his boat 90 km downstream and 70 km upstream, taking 3 hours each time. Find the speed of the stream? Answers.
A) 76 kmph  B) 6 kmph  C) 3.5 kmph  D) 4.5 kmph  E) 4 kmph

Rationale: "speed downstream = d / t = 90 / ( 3 ) = 30 kmph speed upstream = d / t = 70 / ( 3 ) = 23 kmph the speed of the stream = ( 30 - 23 ) / 2 = 3.5 kmph answer : c"
Answer: C