Problem Solving

Hi All,

A car drove from Town A to Town B without stopping. The car traveled the first 40 miles of its journey at an average speed of 25 miles per hour. What was the car's average speed, in miles per hour, for the remaining 120 miles if the car's average speed for the entire trip was 40 miles per hour?

(A) 28
(B) 48
(C) 50
(D) 55
(E) 70

Answer is [spoiler](C)[/spoiler]

I got this question from this link https://www.beatthegmat.com/mba/2011/07/ ... rage-speed.
At one time i was thinking that it is an easy question, but i got confused with the wording of the question. The question says, What was the car's average speed, in miles per hour, for the remaining 120 miles if the car's average speed for the entire trip was 40 miles per hour"

My question is what is the difference between the two average speeds ?

In the explanation i read, This should not be confused with the average of the speeds.
What exactly is the meaning of this ?

Please help me in understanding this wording.

Thanks & Regards
Sachin