Question

Two trains A and B crosses a stationary man in 20 sec. and 1 min 20 sec respectively. The length of train A is 1/3^rd of train B. What is the respective ratio between the speeds of train A to speed of train B?
1. 3 ∶ 4
2. 4 ∶ 3
3. 5 ∶ 2
4. 4 ∶ 5

Answer 1

Correct Answer - Option 2 : 4 ∶ 3

Given:

Time taken by A to cross the man = 20 sec

Time taken by B to cross the man = 1 min 20 sec = 80 sec

Length of train A = 1/3 × length of train B

Formula used:

Time = Distance/Speed

Concept used:

If any train crosses a man/pole or any other vertical object, distance travelled by train is equal to length of the train

Calculations

Let speed of train A be V₁ m/sec

Distance travelled by A to cross the pole = 20V₁

Length of train A = 20V₁

Length of train B = 3 × length of A = 3 × 20V₁ = 60V₁

Speed of train B = 60V₁/80

⇒ 3V₁/4

Ratio of speeds = V₁/(3V₁/4) = 4/3

∴ Required ratio of speeds is 4 ∶ 3