A 250 m long train overtakes a man moving at a speed of 7 km/hr (in same direction) in 50 seconds. How much time (in seconds) will this train take to completely cross another 280 m long train, moving in the opposite direction at a speed of 28 km/hr?

Length of the train = 250 m

Speed of the man = 7 km/hr

Time taken to overtake the man = 50 sec

Relative speed of the train with respect to the man:

$\frac{250}{50} = 5$ m/s

Convert into km/hr:

$5 \times \frac{18}{5} = 18$ km/hr

So, speed of the train:

$18 + 7 = 25$ km/hr

Speed of the other train = 28 km/hr

Since both trains move in opposite directions, relative speed:

$25 + 28 = 53$ km/hr

Convert into m/s:

$53 \times \frac{5}{18} = \frac{265}{18}$ m/s

Total distance to be covered:

$250 + 280 = 530$ m

Required time:

$\frac{530}{265/18}$

$= 530 \times \frac{18}{265}$

$= 36$ seconds

Therefore, the train will take

Answer = 36 seconds