A boat running downstream covers a distance of 40 km in 2 hours while for covering the same distance upstream,it takes 4 hours.What is the speed of the boat in still water ?  Choose one:
A) 4 km/hr	B) 6 km/hr	C) 8 km/hr	D) Data inadequate	E) 15 kmph
Solution   Rate downstream =(40/2)= 
<gadget id="calculator">(40/2)</gadget>
<output>20</output>
20 kmph, Rate upstream=(40/4)= 
<gadget id="calculator">(40/4)</gadget>
<output>10</output>
10 kmph.   ∴ Speed in still water=1/2(20+10) kmph = 15 kmph.   Answer 15 kmph
<result>E</result>
A boat running downstream covers a distance of 40 km in 2 hours while for covering the same distance upstream,it takes 4 hours.What is the speed of the boat in still water ?