A man can row upstream at 12km/hr and downstream at 18 km/hr. The man rowing speed in still water is?

Answer: Option A

Speed of boat in still water = $$\frac{x+y}{2}$$
Where (x = downstream speed) and (y = upstream speed)
∴ Boat's speed
$$\begin{array}{rl}& \text{ = }\frac{18+12}{2}\\ & =\frac{30}{2}\\ & =15km/hr\end{array}$$