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# Quantitative Aptitude :: Problems on Trains

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## Problems on Trains Important Formulas

 1. x km/hr = $$\left[x \times \frac{5}{18} \right]$$ m/s. 2. x m/s = $$\left[x \times \frac{18}{5} \right]$$ km/hr. 3. 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. 4. Time taken by a train of length l metres to pass a stationary object of length b metres is the time taken by the train to cover (l + b) metres. 5. Suppose two trains or two bodies are moving in the same direction at u m/s and v m/s, where u>v, then their relatives speed = (u - v) m/s. 6. Suppose two trains or two bodies are moving in opposite directions at u m/s and v m/s, then their relative speed is = (u + v) m/s 7. If two trains of length a metres and b metres are moving in opposite directions at u m/s and v m/s, then the time taken by the trains to cross each other = $$\frac{(a \ + \ b)}{(u \ + \ v)}$$ sec. 8. If two trains of length a metres and b metres are moving in the same direciton at u m/s and v m/s, then the time taken by the faster train to cross the slower train = $$\frac{(a \ + \ b)}{(u \ - \ v)}$$ sec. 9. If tow trains (or bodies) 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) = (b : a).

Note: It is always advise to convert the unit given in question as per the options. km/hr. to m/sec. or miles/hr.