Speed in still water = 1/2 (11 + 5) kmph = 8 kmph.
In one hour, a boat goes 11 km/hr along the stream and 5 km/hr against the stream. The speed of the boat in still water (in km/hr) is:
a) 3 km/hr
b) 2 km/hr
c) 4 km/hr
d) 6 km/hr
e) 8 km/hr