Correct Answer - Option 3 : 20

**Given:**

The speed of a man traveling on a bicycle is 5 m/sec.

The speed of the train coming from behind is 50 m/sec which crosses him in 10 seconds.

The length of the platform is 550 m.

**Formula Used:**

Relative Speed = Distance/Time

**Calculation:**

Let the length of the train be L.

⇒ L = (50 – 5) × 10

⇒ L = 450 m

As speed of the train is 50 m/sec, then the time(T) taken by the train to cross the platform of length 550 m will be

⇒ (450 + 550) = (50) × T

⇒ T = 1000/50 = 20 sec

**∴ The time taken by the train to cross the platform is 20 seconds.**