A 300 m long train crosses a 900 m long platform in 1 minute 12 seconds. What is the speed of the train (in km/h)?

Introduction / Context:
When crossing a platform, the train must cover its own length plus the platform length. With total time known, speed follows from total distance divided by time, then converted to km/h.

Given Data / Assumptions:

• Train length = 300 m.
• Platform length = 900 m.
• Total time = 72 s.

Concept / Approach:
Total distance = 300 + 900 = 1200 m. Speed in m/s = distance / time; km/h = (m/s)*3.6.

Step-by-Step Solution:
v = 1200 / 72 = 16.666... m/s.In km/h: 16.666... * 3.6 = 60 km/h.

Verification / Alternative check:
At 60 km/h (16.666... m/s), 72 s covers 1200 m as required.

Why Other Options Are Wrong:
45, 50, 54 km/h understate the speed and would take longer than 72 s to cover 1200 m.

Common Pitfalls:
Using only the platform length, ignoring the train's own length.

Final Answer:
60