Because the subjects use completely different skills. Mathematics is
logical and is all about working out equations to find the right answer.
It is very methodical. English is creative and about interpreting
literature and communicating ideas so other people can understand them
and envision it. Any answer can be right as long as you can persuade the
reader. According to biological psychologists, testosterone in males
gives them superior mathematical skills and oestrogen in females gives
them superior verbal skills. And we all know that testosterone and
oestrogen have the opposite effect. However, it should be borne in mind
that some people are good at both subjects.
