Kamran went up a hill at 7.5 km/hr and then came down, covering the same distance, at 5 km/hr. What is his average speed over the entire round trip (in km/hr)?

To calculate the average speed for the entire trip, we need to know the total distance and the total time taken.

1. Let's assume the distance up the hill is 'd' km.

2. Kamran went up the hill at a speed of 7.5 km/hr. So, the time taken to go up the hill is distance/speed = d/7.5 hours.

3. He came down the hill at a speed of 5 km/hr. So, the time taken to come down is distance/speed = d/5 hours.

4. The total distance for the round trip is 2d (up the hill and down the hill).

5. The total time taken for the trip is the time taken to go up the hill plus the time taken to come down the hill. So, the total time = d/7.5 + d/5.

6. The average speed is the total distance divided by the total time. So, the average speed = 2d / (d/7.5 + d/5).

7. If we simplify this equation, we get the average speed = 2 / (1/7.5 + 1/5) = 6 km/hr.

So, Kamran's average speed over the entire round trip is 6 km/hr.