Aptitude Day 283

Problems on Trains 

Formulae:

• Time taken by a train of length ‘l’ meters to pass a pole or standing man = Time taken by the train to cover that same ’l‘ meters.

• Time taken by a train of length ‘l’ meters to pass a stationary object of length ‘a’ meters is the time taken by the train to cover ‘(l+ a)’ meters.

• If 2 trains are moving in the same direction, their relative speed should be their sum and the time taken by the 2 trains to cross each other = Sum of their lengths/ Relative speed.

• If they run in the opposite direction, their relative speed will be their difference and the time taken by the 2 trains to cross each other = Sum of their lengths/ Relative speed.

• If 2 trains start at the same time from points A and B towards each other and after crossing they take a and b seconds in reaching B and A respectively, then 

                                          (A’s speed): (B’s speed) = (b)^1/2 : (a)^1/2