A boat goes 40 km upstream in 8 hours and 36 km downstream in 6 hours. The speed of the boat in still water is

Options

A. 6.5 km/hr
B. 5.5 km/hr
C. 6 km/hr
D. 5 km/hr

Answer

To find the speed of the boat in still water, we will follow these steps:

### Step 1: Calculate the speed of the boat upstream
The boat travels 40 km upstream in 8 hours. To find the speed upstream, we use the formula:

\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]

Substituting the values:

\[ \text{Speed upstream} = \frac{40 \text{ km}}{8 \text{ hours}} = 5 \text{ km/h} \]

### Step 2: Calculate the speed of the boat downstream
The boat travels 36 km downstream in 6 hours. Again, we apply the same formula:

\[ \text{Speed downstream} = \frac{36 \text{ km}}{6 \text{ hours}} = 6 \text{ km/h} \]

### Step 3: Use the formula to find the speed of the boat in still water
The speed of the boat in still water can be calculated using the formula:

\[ \text{Speed in still water} = \frac{\text{Speed downstream} + \text{Speed upstream}}{2} \]

Substituting the speeds we calculated:

\[ \text{Speed in still water} = \frac{6 \text{ km/h} + 5 \text{ km/h}}{2} = \frac{11 \text{ km/h}}{2} = 5.5 \text{ km/h} \]

### Conclusion
The speed of the boat in still water is **5.5 km/h**.

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