A train speeds past a pole in 15 seconds and a platform 100 m long in 25 seconds. Its length is:

Given Data

• Time to pass a pole = 15 s
• Time to pass a 100 m platform = 25 s
• Required: train length (m)

Step 1: Express speed using pole crossing
Let train length = L m. Speed v = L ÷ 15 m/s.

Step 2: Use platform crossing
Distance = L + 100.Time = 25 = (L + 100) ÷ v = (L + 100) ÷ (L/15)⇒ 25 = 15(L + 100)/L ⇒ 25L = 15L + 1500 ⇒ 10L = 1500 ⇒ L = 150 m

Checks & Common Pitfalls

• For a pole, use only the train length to get speed.
• For a platform, add train and platform lengths.
• Avoid mixing units; keep everything in meters and seconds.

Final Answer
The train length is 150 m.