A man travels for 5 hours 15 minutes. If he covers the first half of the journey at 60 km/h and rest at 45 km/hr. Find the total distance travelled by him.

Let the total distance be d. The first half (d/2) at 60 km/h takes d/120 hours. The second half (d/2) at 45 km/h takes d/90 hours. Total time is d/120 + d/90 = 7d/360 = 5.25 hours (5 hours 15 minutes). Solving gives d = 270 km. Note that when distances are equal (not time), you cannot use the simple average speed formula.