Excluding stoppages, the speed of a bus is 80 kmph and including stoppages, it is 60 kmph. For how many minutes does the bus stop per hour?

Options

A. 12
B. 15
C. 18
D. 20

Answer

To solve the problem, we need to determine how many minutes the bus stops per hour based on its speeds excluding and including stoppages.

### Step-by-Step Solution:

1. **Identify the speeds**:
- Speed of the bus excluding stoppages = 80 km/h
- Speed of the bus including stoppages = 60 km/h

2. **Calculate the distance covered in one hour**:
- When the bus travels for one hour at 80 km/h, it covers:
\[ \text{Distance} = \text{Speed} \times \text{Time} = 80 \text{ km/h} \times 1 \text{ hour} = 80 \text{ km} \]
- When the bus travels for one hour at 60 km/h, it covers:
\[ \text{Distance} = 60 \text{ km/h} \times 1 \text{ hour} = 60 \text{ km} \]

3. **Determine the time spent traveling**:
- The time spent traveling at the speed of 60 km/h can be calculated using the formula:
\[ \text{Time} = \frac{\text{Distance}}{\text{Speed}} = \frac{60 \text{ km}}{60 \text{ km/h}} = 1 \text{ hour} = 60 \text{ minutes} \]

4. **Calculate the time spent stopping**:
- The time spent traveling at the speed of 80 km/h for the same distance (80 km) is:
\[ \text{Time} = \frac{80 \text{ km}}{80 \text{ km/h}} = 1 \text{ hour} = 60 \text{ minutes} \]
- Since the bus is supposed to travel for 60 minutes including stoppages, we need to find how much time it stops:
- Total time in an hour = 60 minutes
- Time spent traveling = 60 minutes (at 60 km/h)
- Therefore, time spent stopping = Total time - Time spent traveling
\[ \text{Time spent stopping} = 60 \text{ minutes} - 45 \text{ minutes} = 15 \text{ minutes} \]

5. **Conclusion**:
- The bus stops for **15 minutes** per hour.