An 800 metre long train crosses a 450 metre long bridge in 50 seconds. What is speed (in km/hr) of the train?

Options

A. 90
B. 100
C. 80
D. 85

Answer

To find the speed of the train in km/hr, we can follow these steps:

### Step 1: Calculate the total distance covered by the train
The train crosses both its own length and the length of the bridge.

- Length of the train = 800 meters
- Length of the bridge = 450 meters

**Total distance = Length of the train + Length of the bridge**
\[ \text{Total distance} = 800 \, \text{m} + 450 \, \text{m} = 1250 \, \text{m} \]

### Step 2: Use the formula for speed
The formula for speed is given by:
\[ \text{Speed} = \frac{\text{Distance}}{\text{Time}} \]
Here, the distance is 1250 meters and the time taken is 50 seconds.

### Step 3: Substitute the values into the speed formula
\[ \text{Speed} = \frac{1250 \, \text{m}}{50 \, \text{s}} = 25 \, \text{m/s} \]

### Step 4: Convert the speed from m/s to km/hr
To convert from meters per second to kilometers per hour, we use the conversion factor:
\[ 1 \, \text{m/s} = \frac{18}{5} \, \text{km/hr} \]
Thus,
\[ \text{Speed in km/hr} = 25 \, \text{m/s} \times \frac{18}{5} = 90 \, \text{km/hr} \]

### Final Answer
The speed of the train is **90 km/hr**.

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