A man rows down a river of length 24 km in 4 hours with the stream and returns in 8 hours. What is the speed of the boat in still water?

Correct option is B

Given:

Distance (one way) = 24 km

Time taken downstream = 4 hours

Time taken upstream = 8 hours

We need speed of boat in still water.

Formula Used:

Speed =$$\frac{\text{Distance}}{\text{Time}}$$​​

Downstream speed = Boat speed + Stream speed

Upstream speed = Boat speed – Stream speed

Boat speed in still water $$=\frac{\text{Downstream speed + Upstream speed}}{2}$$​​

Solution:

Downstream speed = $$\frac{24}{4} = 6 \, \text{km/h}$$​​

Upstream speed =$$\frac{24}{8} = 3 \, \text{km/h}$$​​

Speed of boat in still water =$$\frac{6 + 3}{2} = \frac{9}{2} = 4.5 \, \text{km/h}$$​​

The speed of the boat in still water = 4.5 km/h