Two trains are running along a circular path of length 7000 m. These trains started from the same point in opposite direction at the speed of 15 km/h and 13 km/h, respectively. After how much time will they meet each other?

15 minutes

Relative speed in opposite direction = 15 + 13 = 28 km/h = 28 × \(\frac{5}{18}\) m/sec = \(\frac{70}{9}\) m/sec

⇒ Relative speed = \(\frac{Distance}{Time}\)

⇒ \(\frac{70}{9}\) = \(\frac{7000}{Time}\)

⇒ Time = 100 × 9 = 900 seconds = 15 minutes