A boat cover row 12 km upstream in 4 hours and can cover the same distance downstream in 3 hours. What is the speed (in km/hr)) of the boat in still water?

Options

A. 3.5
B. 3
C. 2.5
D. 2

Answer

To solve the problem, we need to find the speed of the boat in still water given the upstream and downstream speeds. Let's break it down step by step.

### Step 1: Identify the given data
- Distance covered upstream = 12 km
- Time taken upstream = 4 hours
- Distance covered downstream = 12 km
- Time taken downstream = 3 hours

### Step 2: Calculate the speed upstream and downstream
- **Speed upstream (U)** = Distance / Time = 12 km / 4 hours = 3 km/hr
- **Speed downstream (D)** = Distance / Time = 12 km / 3 hours = 4 km/hr

### Step 3: Use the formula for speed of the boat in still water
The speed of the boat in still water (B) can be calculated using the formula:
\[ B = \frac{U + D}{2} \]
where U is the speed upstream and D is the speed downstream.

### Step 4: Substitute the values
Substituting the values we calculated:
\[ B = \frac{3 \text{ km/hr} + 4 \text{ km/hr}}{2} \]
\[ B = \frac{7 \text{ km/hr}}{2} \]
\[ B = 3.5 \text{ km/hr} \]

### Final Answer
The speed of the boat in still water is **3.5 km/hr**.

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