In one hour,a boat goes 21 km along the stream and 9 km against the stream.The speed of the boat in still water (in km/hr) is : Select.
A) 3 B) 5 C) 10 D) 9 E) 15
Solution   Speed in still water =1/2(21+9)kmph.= 15 kmph. Answer 15
<result>E</result>
In one hour,a boat goes 21 km along the stream and 9 km against the stream.The speed of the boat in still water (in km/hr) is :