A man rows his boat 110 km downstream and 90 km upstream, taking 3 hours each time. Find the speed of the stream?	Choices:
A) 6 B) 5 C) 7.5 D) 3.5 E) 2.5

Rationale: "speed downstream = d / t = 110 / ( 3 ) = 37 kmph speed upstream = d / t = 90 / ( 3 ) = 30 kmph the speed of the stream = ( 37 - 30 ) / 2 = 3.5 kmph answer : d"
Answer: D