Book for improving problem solving skills for these types of questions

[Kappa123]

I have a test coming, any good book for understand and getting good at these kinds of questions would be great :)
(From the Australian Math Contest)

 

[fresh_42]

This is a difficult question since you usually cannot repeat in a few days what took longer in class, except along the lines of the schoolbook which has been used.

For a general recommendation at this level I would check out these books:
https://openstax.org/subjects