In a city, the local shuttle trains start from and arrive at the station at fixed intervals and run at a uniform speed. A boy was walking down at the railway station at a certain speed. Every half and hour, a local train overtook him and every 20 mins a local train passed him in the opposite direction. Find the time interval between a local train passing at certain point on the railway track and the immediately next local train passing at that point in the same direction ? (Topic - Time, Speed and Distance - Trains)