SQL Function Question - Mailing list pgsql-general

I'm new to SQL and taking a course in it right now.  One of the things that
I need to do for an assignment is display sum, avg, max, and min amounts
multiplied by quantity.  All in one table.  Here is what I'm doing but not
correct for some reason.

select (sum(price)+avg(price)+max(price)+min(price)) * quantity
from order;

I get error - not a single group function.  My book is very limited on the
information so I thought I'd post here.

Thanks!