A 220 m long train passes a signal post in 12 seconds. What is the speed of the train in km/h?

Introduction / Context:
Passing a post uses only train length. Speed equals length divided by time (in m/s), converted to km/h by multiplying by 3.6.

Given Data / Assumptions:

• L = 220 m.
• t = 12 s.

Concept / Approach:
v_mps = 220/12 = 55/3 ≈ 18.3333 m/s. Convert to km/h: v_kmph = v_mps * 3.6.

Step-by-Step Solution:

Verification / Alternative check:
Reverse check: 66 km/h = 18.3333 m/s; in 12 s distance = ~220 m—consistent.

Why Other Options Are Wrong:
54, 60, 69, 72 km/h are off the exact conversion.

Common Pitfalls:
Using 18/5 instead of 5/18 or vice versa incorrectly; rounding too early.

Final Answer:
66 km/h