Error in gnu make?

[j]

I think I have found an error in gnu make....  I want to make a file
of the form-

a.out: a/a.in

b.out: b/b.in

c.out: c/c.in

.
.
.

I would think that I could simplify the above as


filenames=a.out b.out c.out

$(filename): %.out : %/%.in


but this does not work....  instead when I type in "make a.out" I get
the error

 make: *** No rule to make target `a/%.in', needed by `a.out'.  Stop.

question 1- Is this a bug?  Or am I just misunderstanding something?

question 2- Does anyone have a temporary solution for me....  my list
of filenames will be huge and variable, so I don't really want to have
to type out the Makefile (or have some bash script type out the
Makefile) for each set of filenames.

                                                thanks
                                                        -J