There's a community wiki at: Free statistical textbooks that has a nice list of freely available textbooks on statistics. Many of the textbooks that people suggest have exercises at the end of each chapter which is great, but very few of these textbooks have provided solutions to any of the exercises. Sure there may be a variety of reasons for this, but if you are just going through these texts on your own, not in formal course where exercises sets usually have a grader, then that presents an issue as how are you supposed to check your answers.
Posting a new question on here to check to see if you got the right answer is not really practical I think.
Like that these resources are already free, but, and I'm sure others would agree, it's frustrating for a beginner.
e.g. How do i check my answers for @Rob Hyndman book: Forecasting: principles and practice (Hyndman & Athanasopoulos, 2012)
List of solution manuals to books at Free statistical textbooks:
Elements of Statistical Learning by Hastie, Tibshirani, and Friedman