Boat & Stream

When we move upstream the speed gets deducted from the speed of the stream, and when we move down stream our speed gets added to the speed of the stream. Ex-If the speed of the boat in still water is A km/hr. and speed of the streem be B km/hr, then Speed of boat with the stream i.e speed downstream = (A+B)km/hr. And speed of boat against the stream i.e upstream = (A – B) km/hr. Speed of boat in still water =\frac{speed downstream +speed upstream}{2} And Speed of current =\frac{speed downstream - speed upstream}{2} Example- If a boat moves equal distances down stream at a speed 20 km/hr and upstreamat a speed 10 km/hr, then what is the speed of boat in still water. Sol-    Speed of boat in still water =\frac{speed downstream + speed upstream}{2} = \frac{20km/hr+10km/hr}{2} =30/2= 15 km/hr Ex- If a boat moves equal distances down stream   at a speed 20 km/hr and upstream at a speed 10 km/hr,   then what is the speed of current. Sol- Speed of current =\frac{speed downstream - speed upstream}{2} = \frac{20km/hr-10km/hr}{2} =10/2 = 5 km/hr