Two runners, P and Q, start running from the same point on an 800-meter circular track. They run in the same direction at speeds of 12 km/h and 9 km/h, respectively. If they run for 4 hours, how many times will they cross each other?
Show answer & explanation
Correct answer: B
Explanation
Track length = 800 meters = 0.8 km
Relative speed = 12 − 9 = 3 km/h
Relative distance covered in 4 hours = 3 × 4 = 12 km
Relative distance for one crossing = 0.8 km
Therefore, number of crossings = 12/0.8 = 15