A man rows downstream 60 km and upstream 36 km taking 4 hours each time.the speed of the man is:

Options

A. 15 km/h
B. 16 km/h
C. 8 km/h
D. 12 km/h

Answer

To find the speed of the man, we can use the information given about his rowing downstream and upstream. Let's break down the solution step by step.

### Step 1: Understand the Problem
The man rows downstream 60 km and upstream 36 km, taking 4 hours for each journey. We need to find the speed of the man in still water.

### Step 2: Calculate Downstream Speed
The formula for speed is given by:
\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]
For downstream:
- Distance = 60 km
- Time = 4 hours

Using the formula:
\[ \text{Downstream Speed} = \frac{60 \text{ km}}{4 \text{ hours}} = 15 \text{ km/h} \]

### Step 3: Calculate Upstream Speed
For upstream:
- Distance = 36 km
- Time = 4 hours

Using the formula:
\[ \text{Upstream Speed} = \frac{36 \text{ km}}{4 \text{ hours}} = 9 \text{ km/h} \]

### Step 4: Set Up the Equations
Let:
- \( B \) = speed of the man in still water (km/h)
- \( W \) = speed of the water current (km/h)

From the downstream speed, we have:
\[ B + W = 15 \text{ km/h} \quad \text{(1)} \]
From the upstream speed, we have:
\[ B - W = 9 \text{ km/h} \quad \text{(2)} \]

### Step 5: Solve the Equations
Now, we can add equations (1) and (2):
\[ (B + W) + (B - W) = 15 + 9 \]
This simplifies to:
\[ 2B = 24 \]
Dividing both sides by 2:
\[ B = 12 \text{ km/h} \]

### Step 6: Conclusion
The speed of the man in still water is:
\[ \text{Speed of the man} = 12 \text{ km/h} \]