Ramesh rows a boat in still water at a speed of 4.5 km/h to go and to come back. If the river flows at a speed of 1.5 km/h, then, his average speed for the whole journey is:

4 km/h

The correct answer is Option (3) → 4 km/h

$\text{Speed in still water} = 4.5,\ \text{stream} = 1.5$

$\text{Downstream speed} = 4.5 + 1.5 = 6$

$\text{Upstream speed} = 4.5 - 1.5 = 3$

$\text{Average speed} = \frac{2 \times 6 \times 3}{6 + 3}$

$= \frac{36}{9} = 4$

$\text{Average speed} = 4\ \text{km/h}$