A 100 m long train overtakes a man moving at a speed of 9 km/hr (in same direction) in 30 seconds. How much time (in seconds) will this train take to completely cross another 220 m long train, moving in the opposite direction at a speed of 51 km/hr?​

Correct option is D

Given:

Length of the first train = 100 m

Speed of the man = 9 km/hr

Time taken to overtake the man = 30 seconds

Length of the second train = 220 m

Speed of the second train = 51 km/hr

The trains are moving in opposite directions.

Formula Used:

Relative speed = $$\frac{\text{Length of train}}{\text{Time taken}}$$​​

Solution: 

speed of train - 9  = $$\frac{100}{30} \times \frac{18}{5}$$ 

Speed of train = 12 + 9 = 21 km/h 

Now time taken to cross another train in opposite direction;

time = $$\frac{100+220}{(21+51)\times \frac5{18}} = 16 \ sec$$​