Question

A motorboat can travel in still water at the speed 15 km/h, while the speed of the current is 3 km/h. Time taken by boat to go 36 km upstream is:

• A. 2 hr
• B. 3 hr
• C. 12 hr
• D. 18 hr

Answer 1

Answer: (B)

3 hr

Answer 2

The boat is moving at $15\ km/h$ in still water and the current is moving at $3\ km/h$
Therefore, the boat's effective speed upstream = $15\ km/h - 3\ km/h$ = $12\ km/h$
Now, Time taken by boat to go 36 km upstream = $\frac {36\ km}{12\ km/h}$ = 3 hr

So, the correct option is (B): 3 hr.