Thoughts on Mathematics of Statistics by Kenney? This book is written in 1939. It's available here on archive.org. 
Would you recommend this as an introduction to the mathematics of statistics for beginners?
 A: I wouldn't. The word "likelihood" appears only two times in the whole book (both volumes). Also, the anti-Bayesian criticisms are definitely dated. As my first book, I would use DeGroot-Schervish.
A: What's your background? Casella & Berger is by far my favourite book on mathematical statistics (there's a very cheap international edition). There's Hogg Craig too, which you can use as second source since it's got a similar scope.
A: If you want books on mathematical statistics at a graduate level, try


*

*Essentials Statistics by Boos and Stefanski

*Statistical Theory: a concise introduction by Abramovich and Ritov

*Understanding Advanced Statistical Methods by Westfall and Henning

*Probability for Statistics and Machine Learning by Das Gupta

*All of Statistics by Wasserman

A: If you like old books, then I'd recommend Feller's classic text. It has all the math you need, and explains all very clearly.
A: If you're looking for a free online introductory statistics textbook, may I recommend to have a look at OpenIntro Statistics? Not only it's well-written and quite easy to understand, but it also has nice online interactive exercises in R available at datacamp.org 
