A boat running downstream covers a distance of 12 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 the correct choice from the following options:
A) 4.5 km/hr
B) 6 km/hr
C) 8 km/hr
D) Data inadequate
E) None of these
Solution   Rate downstream =(12/2)= 
<gadget id="calculator">(12/2)</gadget>
<output>6</output>
6 kmph, Rate upstream=(12/4)= 
<gadget id="calculator">(12/4)</gadget>
<output>3</output>
3 kmph.   ∴ Speed in still water=1/2(6+3) kmph = 4.5 kmph.   4.5 km/hrnswer 4.5 km/hr
<result>A</result>
A boat running downstream covers a distance of 12 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 ?