Mathematics undergraduate at St. John’s vs King’s

I’m a 17 year old student residing outside the UK, and I’ve been quite keen for a while to apply to Cambridge for pure mathematics. For reference, my grades are all A*s in everything but computer science. I’ve finished the further math syllabus (although I’m not set to give the exam till next year) , and it’s become a pastime of mine to occasionally solve STEP 3 problems. I’m generally able to solve almost all of the STEP pure maths questions (although I’m quite bad at the mechanics part), which I’m hoping is a indicator of being able to give a strong performance at the interview. However, I don’t know whether to apply to King’s, or St John’s. Afaik King’s is less competitive for math, but St. John’s has separate pure and applied interviews, which would hopefully mean the chance I get asked a mechanics question is lower. I don’t have any math Olympiad experience so I’d also like to know if that makes a difference. TLDR; I have good grades and am able to fully solve pretty advanced STEP questions, and don’t know whether to apply to St. John’s or King’s.

I’m a 17 year old student residing outside the UK, and I’ve been quite keen for a while to apply to Cambridge for pure mathematics. For reference, my grades are all A*s in everything but computer science. I’ve finished the further math syllabus (although I’m not set to give the exam till next year) , and it’s become a pastime of mine to occasionally solve STEP 3 problems. I’m generally able to solve almost all of the STEP pure maths questions (although I’m quite bad at the mechanics part), which I’m hoping is a indicator of being able to give a strong performance at the interview. However, I don’t know whether to apply to King’s, or St John’s. Afaik King’s is less competitive for math, but St. John’s has separate pure and applied interviews, which would hopefully mean the chance I get asked a mechanics question is lower. I don’t have any math Olympiad experience so I’d also like to know if that makes a difference. TLDR; I have good grades and am able to fully solve pretty advanced STEP questions, and don’t know whether to apply to St. John’s or King’s.

Apply to both then decide

I think OP is referring to King's College, Cambridge and St John's College, Cambridge. Unless OP is an organ scholar, it is generally not possible to apply to more than one Oxbridge college in a given year.