[erlang-questions] Newbie Question about io:format

[Richard A. O'Keefe]

On 21/02/17 10:15 PM, Hakim Fajardo wrote:
(simplified):

prices([]) ->
     io:format("List is empty~n");
prices(L) when is_list(L) ->
     io:format("The average equals ~n", lists:sum(L)/length(L)).
               ^^^^^^^^^^^^^^^^^^^^^^^

% man io
        format(Format, Data) -> ok
                  Data = [term()]

The second argument of io:format/2 should be a list.

What part of the format says to expect a number?
What part of the format says how to print a number?