Level 3 3 m
Jake walks to school at an average speed of 4 km/h every day. One day, after walking a distance of 1 km, he realised that his watch was slow. So, he ran at a constant speed and managed to reach his school just on time. Later, he calculated that if he had run at this speed right from the start of the journey, he would have reached his school 5 minutes earlier. What was his running speed?