i know 2 people who got 99.95, one guy studied 2hrs a day the other 3 hrs a day. That being said they also paid attention in school and spent lunch times and free periods studying as well.
for Chemistry i have one of those HSC books with the questions and answers so whilst i was studying a topic if i had a good understanding of the content i would go through the HSC questions then check the marking criteria and sample responses to make sure i did everything correct. Once i did...
for b) to produce the first 15 houses the clothing goes from 50 to 40. Therefore there had been a decrease of 10 clothing. As a result to produce the first 15 houses you had to forego 10 clothing.
c) To produce 15 houses you forego 10 clothing therefore the ratio is 15:10 if you simplify it...