[plt-scheme] science fair help

I have a student who's doing a science fair project and needs to find
the average for each location in a bunch (number unspecified) of
lists.

For example, given

(list 1 3 5 7) (list 2 1 3 3) (list 3 8 1 5)

he'd like

(list 2 4 3 5)

I can write the function pretty easily in Module by writing an average
function that takes a variable number of arguments, but my attempts to
do it in Intermediate or Advanced are pretty complicated. Is there a
fairly easy way to do it in the teaching languages that I'm missing?
If not, I can just put together a teachpack for him that provides that
function so he can use it.

Todd