If a bus covers a distance excluding stoppages, its usual speed is 80 km/h and including stopages it is 60 km/h. For how many minutes does the bus stop per house ?

Options

A. a)10 min
B. b)20 min
C. c)15 min
D. d)30 min

Answer

To solve the problem of how many minutes the bus stops per hour, we can follow these steps:

### Step 1: Understand the given information
- The usual speed of the bus (excluding stoppages) = 80 km/h
- The speed of the bus including stoppages = 60 km/h

### Step 2: Identify the formula for stoppage time
The stoppage time can be calculated using the formula:
\[ \text{Stoppage Time} = \frac{\text{Usual Speed} - \text{Speed Including Stoppages}}{\text{Usual Speed}} \]

### Step 3: Substitute the values into the formula
Substituting the values we have:
\[ \text{Stoppage Time} = \frac{80 \text{ km/h} - 60 \text{ km/h}}{80 \text{ km/h}} \]

### Step 4: Calculate the difference in speeds
Calculate the difference:
\[ 80 \text{ km/h} - 60 \text{ km/h} = 20 \text{ km/h} \]

### Step 5: Substitute the difference back into the formula
Now substituting back:
\[ \text{Stoppage Time} = \frac{20 \text{ km/h}}{80 \text{ km/h}} \]

### Step 6: Simplify the fraction
Simplifying the fraction:
\[ \text{Stoppage Time} = \frac{1}{4} \text{ hours} \]

### Step 7: Convert hours into minutes
Since 1 hour = 60 minutes, we convert \(\frac{1}{4}\) hours into minutes:
\[ \text{Stoppage Time in minutes} = \frac{1}{4} \times 60 \text{ minutes} = 15 \text{ minutes} \]

### Final Answer
The bus stops for **15 minutes** per hour.

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