Train 'M' can cross a pole in 10 seconds and a 200 metres

Solution

Let the length and the speed of the train 'M' be 'x' metres and 's' m/s.
ATQ,
(x/s) = 10
So, 'x' = 10s.........(i)
Also, {(x + 200) ÷ s} = 15
Or, 10s + 200 = 15s [from equation (i)]
Or, 200 = (15s - 10s)
Or, 's' = (200/5) = 40
Length of train 'M' = (10 × 40) = 400 metres
So, length of train 'N' = (400 × 0.50) = 200 metres
Let the speed of train 'N' be 'n' m/s.
ATQ,
(400 + 200) ÷ (n - 40) = 15
Or, 600 = 15 × (n - 40)
Or, (n - 40) = 40
So, 'n' = 40 + 40 = 80
Therefore, speed of train 'N' = 80 m/s