# Quantitative Aptitude - Problem On Trains - Formula & Concept Tutorial

- To convert
**km/hr**to**m/sec**

**x km/hr** = ( x * 5/18) **m/sec**

- To convert m/sec to km/hr

**x m/sec** = (x * 18/5) **km/hr**

- Time taken by a train of length l metres to pass a pole or a standing man or a signal post is equal to the time taken by the train to cover l metres.
- Time taken by a train of length l metres to pass a stationary object b metres is the time taken by the train to cover ( l + b ) metres.
- Suppose two trains or two bodies are moving in the same direction at u m/s and v m/s , then their relative speed is ( u - v ) m/s
- Suppose two trains or two bodies are moving in the opposite direction at u m/s and v m/s , then their relative speed is ( u + v ) m/s
- If two trains of length a metres and b metres are moving in opposite direction at u m/s and v m/s , the time taken by train to cross each other is sec.
- If two trains of length a metres and b metres are moving in the same direction at u m/s and v m/s , then the time taken by the faster train to cross the slower train is sec.
- If two trains start at the same time from points A and B towards each other and after crossing they take a and b sec in reaching B and A respectively, then:

A’s Speed : B’s Speed =