Maths, Physics, Chemistry - they're brilliant because there is a right or wrong answer... right? None of that mumbo-jumbo 'interpretation' rubbish that you get in the Humanities. When you've done a good job you know you've done a good job. So all you have to do is figure out what you're going to be asked in your interview at Cambridge or Oxford and you'll be laughing.
Cambridge and Oxford aren't really like that - even to the extent that a student who can answer a difficult question with the correct numerical answer on the spot in a second isn't necessarily as interesting as the student who takes three or four minutes working it out on paper, who then comes to the right conclusion. You cannot learn any right answers, or predict the questions, but you can get used to approaching very difficult questions and having a go. We asked our Maths expert to do exactly this, with a few, real past Oxford and Cambridge interview questions.