hardest classes im finishing degree applied mathematics requires take lot credits hours wide range stem fields ranking list difficulty field  computer science quite difficult competitive high attrition requires creativity ability visualize abstract data structures  engineering similar computer science less abstract  pure mathematics very abstract many paths right conclusion physics  grounded problems hard favorite field computational practicality  economics you need apt arithmetic manipulating graphs chemistry there lot concepts equations much creativity least lower level  biology  mostly concepts tricky nothing practice cant overcome considering including humanities philosophy would near top abstract similar pure maths is