I suggest if u cannot do probability just drop down to general or drop maths altogether because probability is the most logical sub-section of mathematics and if you cannot do it then u cannot do maths cause maths is ALL LOGIC, & i have bad news 4 u, u cannot GUESS your way through the HSC!!!!!
yes i am, i have notes on cosi that answers your question, it was an assesment task i did and i hav included to related texts that i describe qiute thoughroughly
go to http://www.tripod.com/essays/cosi
good luck
go to http://www.tripod.org/hsc/notes/aos
this is my website where i have answered your question in an assesment task in essay form, i posted it up a couple of months ago.
Good luck