I wasnt looking at percentages. Thats just what I estimate he will get in those subjects based on his rankings. Getting 97 overall in physics and 98 in agriculture is huge, and given their scaling, they will probably count towards his ATAR. Also, since he is doing 10 units this year, 4 wont count. I reakon that economics and his worst 2 units of maths will be excluded. So his score in the remaining six units which count will probably be in the mid to late 90's. Thats mainly why I estimated him so high.
Just adding on to my initial post, its really difficult to estimate ATARs from people who go to James Ruse, because the school always does so much better then the rest of the state. Like the difference between Ruse and the second best school is way larger then the difference between the second best school and third best. So getting a good idea of exactly where a ruse student sits based on there rankings is very difficult