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

sub prefix:<r/+> (@_) { reduce &(-> $x, $y { $x + $y }), @_ }
r/+(1, 2, 3, 4 ,5) # => 15
sub prefix:<//?> (@_) { (r/+@_) / $(@_) }
//?(1, 2, 3, 4, 5) # => 3

An operator for ^_everything!