An aeroplane covers 2500km, 1200km and 500km at the rate of 500km/hr, 400km/hr and 250km/hr respectively. Find its average speed for the whole journey.

To find the average speed for the entire journey, you can use the formula for average speed:

Average Speed = Total Distance / Total Time

First, you need to calculate the total distance covered and the total time taken for each segment of the journey, and then add them up.

For the first segment of 2500 km at 500 km/hr:
Time = Distance / Speed = 2500 km / 500 km/hr = 5 hours

For the second segment of 1200 km at 400 km/hr:
Time = Distance / Speed = 1200 km / 400 km/hr = 3 hours

For the third segment of 500 km at 250 km/hr:
Time = Distance / Speed = 500 km / 250 km/hr = 2 hours

Now, add up the total distance and total time for the entire journey:

Total Distance = 2500 km + 1200 km + 500 km = 4200 km
Total Time = 5 hours + 3 hours + 2 hours = 10 hours

Now, calculate the average speed:

Average Speed = Total Distance / Total Time
Average Speed = 4200 km / 10 hours
Average Speed = 420 km/hr

So, the average speed for the whole journey is 420 kilometers per hour.