A boy can swim in still water at a speed of the 10 km/hr . If the speed of the current would have been 5 kmph , then the boy could swim 60 km

Options

A. upstream in 4 hour
B. downstream in 12 hours
C. upstream in 6 hours
D. downstream in 4 hours

Answer

To solve the problem step by step, let's break it down:

### Step 1: Identify the speeds
- The speed of the boy in still water = 10 km/hr
- The speed of the current = 5 km/hr

### Step 2: Calculate the effective speeds
- **Downstream speed** (when swimming with the current) = Speed of boy + Speed of current
\[ \text{Downstream speed} = 10 \text{ km/hr} + 5 \text{ km/hr} = 15 \text{ km/hr} \]

- **Upstream speed** (when swimming against the current) = Speed of boy - Speed of current
\[ \text{Upstream speed} = 10 \text{ km/hr} - 5 \text{ km/hr} = 5 \text{ km/hr} \]

### Step 3: Calculate the time taken to swim 60 km downstream
- Using the formula: Time = Distance / Speed
\[ \text{Time downstream} = \frac{60 \text{ km}}{15 \text{ km/hr}} = 4 \text{ hours} \]

### Step 4: Calculate the time taken to swim 60 km upstream
- Using the same formula:
\[ \text{Time upstream} = \frac{60 \text{ km}}{5 \text{ km/hr}} = 12 \text{ hours} \]

### Step 5: Conclusion
- The boy can swim 60 km downstream in 4 hours and upstream in 12 hours.

### Final Answer
- The correct option based on the calculations is that the boy swims downstream in 4 hours.

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