Question

In one hour, a boat goes 11 km/hr along the stream and 5 km/hr against the stream. The speed of the boat in still water (in km/hr) is :

• A. 3 km/hr
• B. 8 km/hr
• C. 5 km/hr
• D. 9 km/hr

Answer 1

Answer:

B. 8 km/hr

The speed of the boat in still water is 8 km/hr.

To find the speed of a boat in still water when the downstream and upstream speeds are given, use the following formula:
$\text{Speed in still water} = \frac{\text{Speed Downstream} + \text{Speed Upstream}}{2}$

• Speed downstream (along the stream) = 11 km/hr

• Speed upstream (against the stream) = 5 km/hr

• Calculation:
  $\frac{11 + 5}{2} = \frac{16}{2} = 8 \text{ km/hr}$