Correct Answer - Option 2 : 15 km/hr

**Given:**

Length of train = 125 m

Time to cross tree = 30 sec

**Formula: **

Time to cross the tree = length of train/speed of train

1 m/sec = 18/5 km/hr

**Calculations:**

S = D/T = 125/30 m/sec

⇒ (125/30) × (18/5)

⇒ 15 km/hr

**∴**** Speed of train is 15 km/hr**