In one hour, a boat goes 11 km along the stream and 7 km against the stream. the sped of the boat in still water (in km/hr) is :  Choose one
A) 3
B) 5
C) 8
D) 9
E) 10
Solution   Speed in still water= 1/2(11+7) km/hr= 9kmph. Answer 9
<result>D</result>
In one hour, a boat goes 11 km along the stream and 7 km against the stream. the sped of the boat in still water (in km/hr) is :