Hi, there.

The prompt is very poorly worded.
An airplane travels distance 2500 km,1200 km,500 km at the rate of 500 kmphr, 400kmphr, 200kmphr. Find the average speed?

I assume what is meant is:
An airplane took a flight consisting of three segments.
(a) first segment was 2500 km at an average speed of 500 kmphr
(b) second segment was 1200 km at an average speed of 400 kmphr
(c) third segment was 500 km at an average speed of 200 kmphr
What is the average speed of the entire trip?

So, to find average speed, we divide total distance by total time.

The total distance = 2500 + 1200 + 500 = 4200 km

The time of segment #1 is t1 = 2500 km/500 kph = 5 hr
The time of segment #2 is t2 = 1200 km/400 kph = 3 hr
The time of segment #3 is t3 = 500 km/200 kph = 2.5 hr

Total time = t1 + t2 + t3 = 5 + 3 + 2.5 = 10.5 hr

Average velocity = (total distance)/(total time) = 4200 km/10.5 hr = 400 kph

Here's a related question, for more practice.

https://gmat.magoosh.com/questions/5

Does all this make sense? Please let me know if anyone reading this has any further questions.

Mike