Rajadhani Express and Duronto Express running in opposite direction cross a man standing on the platform in 28 seconds and 32 seconds respectively. The trains cross each other in 40 seconds. What is the ratio of speeds of Rajdhani Express and Duronto Express?

Question

Solutons With Key Points

Answer- B

Let the trains are moving at X m/s and Y m/s respectively.

So, length of the first train: (speed) * (time taken to cross the standing man) = X * 28 seconds= 28X

In a similar way, length of second train: (speed) * (time taken to cross the standing man) = Y * 32 seconds= 32Y

The trains take 40 seconds to cross each other = total distance/ relative speed

Total Distance = sum of the length of trains (28X + 32Y)

Relative Speed = X + Y, as the trains are moving in the opposite direction.

40 = (28X + 32Y)/ (X + Y)

40 X + 40 Y = 28X + 32 Y

12 X = -8Y

3X=-2Y

X:Y = 2:3

removing - sign because speed cannot be negative.