1) si estudias…
aprobarás
IF + PRESENTE SIMPLE --- FUTURO
SIMPLE (= WILL not + V infinitivo)
IF YOU STUDY --- YOU WILL PASS
YOU WILL PASS --- IF YOU STUDY.
2) si
estudiaras… aprobarías
IF + PASADO SIMPLE --- WOULD not + V infinitivo
IF YOU STUDIED --- YOU WOULD PASS
YOU WOULD PASS--- IF YOU STUDIED
3) si hubieras
estudiado --- habrías aprobado
IF + PASADO PERFECTO (= HAD + V participio) --- WOULD not HAVE + V participio
IF YOU HAD
STUDIED --- YOU WOULD HAVE
PASSED
YOU WOULD HAVE PASSED --- IF YOU HAD STUDIED