In http://sqlcourse2.com/groupby.html Q3:
"How many orders did each customer make? Use the items_ordered table. Select the customerid, number of orders they made, and the sum of their orders. Click the Group By answers link below if you have any problems."

the answer for the sum of the orders is given as sum(price) when it would seem to be more sensible to calculate sum(quantity*price). Which was intended, and what is correct?