omg i hated this topic so much
best thing to do would defs be lots and lots of practice questions. the more you do the better. you can't ever do enough of them.
it's not 50%, but yeh it is a major part of the HSC, and is often a diffferentiating factor between band E4 and Band E3 students [along with circle geo, perms and coms, etc]
my advice: do heaps of questions from past papers till you understand it anda re getting all q's right