I have experienced this.
For that, you need to be strong at class 8 maths not just from school's syllabus perspective but also from Olympiad perspective.
For science, they are not going to ask u of class 9 because science of class 8 and 9 is not related. class 8 science is related to class 10 and class 9 science is related to class 11 and so on- alternate linking. But, you need to look a little at some starting lessons some like that of physics, - 'motion'. It would be helpful because the concepts in that lesson are some of the basic ones.