how do I average in scheme?

im learning scheme and im not very good its my first languages what am i doing wrong

(define (average nums)
   (/ (+ (car nums) (average (cdr nums))) 2))

then i do (average (list 2 3 4 5 6)) but it doesnt work
also how can i do that (average 2 3 4 5 6) gives me the average without doing a list?

please help

>>23
Better:

sub prefix:<r/+>(@_){reduce &infix:<+>, @_}
sub prefix:<//?>(@_){(r/+@_)/$(@_)}
//?(1,2,3,4,5)