Question

A takes 20 hours to travel a distance of 320 km and B travels 320 km in 40 hours. If they are 640 km apart from each other then find the time taken by A and B to cross each other when they are running in the opposite direction.
1. (60/7) hr
2. (80/3) hr
3. (40/7) hr
4. None of the above

Answer 1

Correct Answer - Option 2 : (80/3) hr

Given:

A takes 20 hours to travel a distance of 320 km

B travels 320 km in 40 hours.

Formula used:

Speed = Distance/Time

Relative speed = (v₁ + v₂), when objects run in opposite direction

Where,

v₁ → Speed of first object

v₂ → Speed of second object

Calculation:

Speed of A = 320/20 = 16 km/h

Speed of train B = 320/40 = 8 km/h

Relative speed for opposite direction = 16 + 8 = 24 km/h

Required time = 640/24 = (80/3) hours

∴ Time taken by A and B to cross each other is (80/3) hours