Best books for hard ACT Math questions

I’m trying to prep for the ACT and my practice scores under time are always from 27-31, usually 30. Besides doing practice tests, are there any good books for hard ACT Math questions, as the last ten I usually get half of them right, if I don’t run out of time. Even un-timed I can’t solve half of them.
Thanks

You should practice with those problems and understand the mistakes that you did on the tests. Learn how to do them and not to make them again. The Real ACT book is the best book available. Always practice and study from the people who made the test. Good Luck!

Princeton Review Cracking the ACT & Math Workout and Barrons ACT Math Workbook & ACT 36 can help you get the math up. Use them to get the strategies down and then implement what you learned by practicing with the red book.