A boat running downstream covers a distance of 20 km in 2 hours while for covering the same distance upstream, it takes 5 hours. What is the speed of the boat in still water?
Answer: B
Rate downstream = (20/2) kmph = 10 kmph;
Rate upstream = (20/5) kmph = 4 kmph
Speed in still water = 1/2 (10 + 4) kmph = 7 kmph