Multiple choice

If a train takes $1$ second to cross a telegraph post and $3$ seconds to cross a platform $300$ metres long, then the length of the train (in metres) is

  1. $100$
  2. $150$
  3. $200$
  4. $300$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Let train length be L and speed be v. Crossing post: L/v = 1, so L = v. Crossing platform: (L + 300) / v = 3. Substitute L = v: (v + 300) / v = 3. v + 300 = 3v, 2v = 300, v = 150. Since L = v, L = 150.

AI explanation

Let the train's length be L meters and its speed be S m/s. Crossing a telegraph post gives S equals L. Crossing a 300 m platform gives the equation 3 times S equals L plus 300. Substituting L for S results in 3L equals L plus 300, so the train's length is 150 meters.

Keep practicing — related questions