Train 'A' crosses a pole in 35 seconds and takes 40

Solution

Let the length of train 'A' be 'd' metres. So, distance covered by train 'A' in 35 seconds = 'd' metres And distance covered by train 'A' in 40 seconds = (d + 120) metres So, distance covered by train 'A' in (40 - 35) i.e., 5 seconds = d + 120 - d = 120 metres So, speed of train 'A' = (120/5) = 24 m/s So, length of train 'A' = 24 X 35 = 840 metres Length of train 'B' = (840/2) = 420 metres So, speed of train 'B' = (420 + 210) ÷ 30 = 21 m/s So, time taken by trains 'A' and 'B' to cross each other = (840 + 420) ÷ (24 + 21) = 1260 ÷ 45 = 28 seconds