The downstream speed of a boat is 20 km/hr and the speed of current is 5 km/hr. What is the total time (in hours) taken by the boat to cover 80 km upstream and 100 km downstream?

Options

A. 6
B. 13
C. 10
D. 12

Answer

To solve the problem, we need to determine the total time taken by the boat to cover 80 km upstream and 100 km downstream, given the downstream speed of the boat and the speed of the current.

### Step-by-Step Solution:

1. **Identify the given values:**
- Downstream speed of the boat = 20 km/hr
- Speed of the current = 5 km/hr

2. **Calculate the speed of the boat in still water:**
- Speed of the boat in still water = Downstream speed - Speed of current
- Speed of the boat in still water = 20 km/hr - 5 km/hr = 15 km/hr

3. **Calculate the upstream speed of the boat:**
- Upstream speed = Speed of the boat in still water - Speed of current
- Upstream speed = 15 km/hr - 5 km/hr = 10 km/hr

4. **Calculate the time taken to cover 80 km upstream:**
- Time = Distance / Speed
- Time taken upstream = 80 km / 10 km/hr = 8 hours

5. **Calculate the time taken to cover 100 km downstream:**
- Time taken downstream = 100 km / 20 km/hr = 5 hours

6. **Calculate the total time taken for the journey:**
- Total time = Time taken upstream + Time taken downstream
- Total time = 8 hours + 5 hours = 13 hours

### Final Answer:
The total time taken by the boat to cover 80 km upstream and 100 km downstream is **13 hours**.