Undoubtedly, the experimental class is more difficult. First of all, because the questions inside are real questions in the exam, rather than adapted questions, they are more restored and more difficult, and if given, the answer is to help many students when some questions are not understood or can't be done. As long as you look at the answers, your thinking will get a basic improvement, so I personally recommend this workbook, especially for a student who is about to face an exam.