What is the average gradepoint for any students enrolled in courses?
select avg(t2.gradepoint) from enrolled_in as t1 join gradeconversion as t2 join student as t3 on t1.grade = t2.lettergrade and t1.stuid = t3.stuid
What is this for students with last name Smith?
select avg(t2.gradepoint) from enrolled_in as t1 join gradeconversion as t2 join student as t3 on t1.grade = t2.lettergrade and t1.stuid = t3.stuid where t3.lname = "Smith"