Two trains of equal length are running on parallel lines in the same direction at speeds of 100 km/h and 66 km/h. The faster train passes the slower train in 18 seconds. The length of each train is:

Correct option is B

Given:

Speeds: 100 km/h (fast), 66 km/h (slow)

Direction: Same

Time to overtake completely = 18 s

Formula Used:

$$\text{Distance} = \text{Speed} \times \text{Time}$$​

Solution:

Relative speed = (100 - 66) = 34 km/h

Lengths of trains are equal = L each​

Distance covered during overtaking = sum of lengths = L + L = 2L

Distance to pass completely =2L= relative speed ×time

$$= 34 \times \frac{5}{18} \times 18= \frac{170}{18} \times 18 = 170$$ m​
Now,

2L = 170

L = 85 m.