Two trains of length 127 mt. and 98 mt. are moving in opposite directions with speed 35 km/hr and 55 km/hr respectively. After meeting they will cross each other in

Work it the standard way. When two trains move in opposite directions, their speeds add up, so relative speed = 35 + 55 = 90 km/hr. Convert to m/s by multiplying by 5/18: 90 × 5/18 = 25 m/s.

Crossing means the front of one train has to travel past the entire length of the other, so the distance to cover is the sum of both lengths: 127 + 98 = 225 m. Time = 225 / 25 = 9 seconds. Option C is correct.

• A (6 s): would need a relative speed of 37.5 m/s, which the given speeds do not produce.
• B (8 s): implies about 28.1 m/s, which points to a wrong addition or a conversion slip.
• D (10 s): implies 22.5 m/s, which comes from subtracting the speeds or converting wrongly.

Core concept: relative speed in opposite directions and the 5/18 conversion. This sits under quantitative aptitude and basic mechanics, and the same logic drives overtaking and crossing problems in reasoning sections.

Trap: subtracting speeds for opposite motion, or adding them for same-direction motion, and forgetting to add both train lengths.