On her way home from work, janet drives through several toolbooths. Is there a pair of these tollbooths that are less than 10 miles apart?

1. The first and the last tollbooths are 25 miles apart.

2. Janet drives through 4 tollbooths on her way from work.

I am confused about C and E in this question. Gmatprep's answer is C.

What is the highlight in this question that the distance between the towns is additive or cumulative? To me, they can all be 10 miles apart. When I got this question in GMATprep it reminded me of 1) Question 40 DS, OG12 page 276. In this question before I looked at numbers correctly, i thought the distance from R to U is additive. 2) The RTD question 104 DS, OG12 page 282, if I am not told that the average speed of the train was constant, never assume.

Why does the same reasoning not work here?

Cheers!!!