In one hour, a boat goes 15 km along the stream and 5 km against the stream. the sped of the boat in still water (in km/hr) is :
Options:  A) 3  B) 5  C) 8  D) 9  E) 10
Solution   Speed in still water= 1/2(15+5) km/hr= 10kmph. Answer 10
<result>E</result>
In one hour, a boat goes 15 km along the stream and 5 km against the stream. the sped of the boat in still water (in km/hr) is :