Two trains, one 153 m long and the other 127 m long, coming from opposite directions crossed each other in 7.2 seconds. The combined speed of the two trains every hour would then be:

Options

A. 140 km/h
B. 105 km/h
C. 70 km/h
D. 280 km/h

Answer

To find the combined speed of the two trains, we can follow these steps:

### Step 1: Determine the lengths of the trains
- Length of the first train = 153 meters
- Length of the second train = 127 meters

### Step 2: Calculate the total distance covered when the trains cross each other
- Total distance = Length of first train + Length of second train
- Total distance = 153 m + 127 m = 280 meters

### Step 3: Identify the time taken to cross each other
- Time taken to cross each other = 7.2 seconds

### Step 4: Calculate the relative speed of the trains
- Relative speed = Total distance / Time taken
- Relative speed = 280 m / 7.2 s

### Step 5: Perform the division to find the speed in meters per second
- Relative speed = 280 / 7.2 = 38.89 m/s (approximately)

### Step 6: Convert the speed from meters per second to kilometers per hour
- To convert m/s to km/h, multiply by 18/5.
- Speed in km/h = 38.89 m/s × (18/5)

### Step 7: Calculate the final speed in kilometers per hour
- Speed in km/h = 38.89 × 3.6 = 140 km/h (approximately)

### Final Answer:
The combined speed of the two trains is **140 km/h**.

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