Hey Yash , think of it like this..
>When you depart from point 'A' following the GC track towards 'B', the GC track is 096, and on reaching pont 'B' the GC track would be 104. (since Convergency is 8, and remember when flying eastward in the Northern Hemisphere GC track increases). So when you are at the midpoint on your GC journey from 'A' to 'B' , the GC track would be 100. (which is what they are trying to say when they mention the average GC track is 100)