They only take the best 2 UNITS of english. So if you do advanced and extention, and your advanced marks are better than extention, they wont take your extention marks into account. The whole paper is out of 45, and the entire exam for english is out of 105.
That isn't true. They take AT LEAST your best 2 units of English. If you did English Ext and had 11 units, and English Ext was your worst unit then only your 2 units of Advanced would count. If you did worst in Advanced (out of your 11 units), 1 unit of Advanced would count and 1 unit of Extension. If neither are your worst, then all 3 units of English will be counted and one of your other subjects will be half counted. Similarly, if you do 4u English and screwed up Advanced (as your worst subject) having done 12 units then none of Advanced would count.
To clarify for the thread. Every section is counted. It is all double marked. The raw marks are scaled based on the overall performance of your year, which is usually reflective of the difficulty of the subject and, even if you are terrible at a section, attempting a section is easy marks. All of this is over though, good luck to the year of 2012.