My book says that
is a structure used to say
A accounts for [fraction] of B
So far, so good. But it also provides the following two alternative structures, which bother me:
What I don't really understand is why in the first structure
B, that's supposed to be the whole which
A is a part of, is marked with the particle
に is used in the other two structures.
Moreover, I could not find any example that uses the second structures.
Are these alternative structures commonly used? And how can I wrap my head around which of the whole and the part is marked by what particle?