How many instructors in the physics department make less than that?
Select count ( * )  from instructor where dept_name  =  'Physics' and salary <  ( SELECT avg ( salary )  FROM instructor WHERE  dept_name   =   'Physics' ) 
instructors in the physics department = WHERE dept_name = 'Physics'; make less than = salary <; how many = COUNT(*); less than average salary in the physics department = salary < (SELECT AVG(salary) FROM instructor WHERE dept_name = 'Physics')