# Good free online PDFs for probability and statistics (with practice problems and answers)?

I'd like to rebuild from the ground up and really make sure I have a strong grasp on probability and statistics.

I am able to compute answers in a pinch but I'd like a more formal understanding so I can really ensure I am being systematic about it. For example I have no idea what a probability mass/density function is.

Are there any good resources that go over all the basics and fundamentals while also providing answers to check my work against?

• Want to go little recent, here is the 11th edition (for approx $15): amazon.com/Elementary-Statistics-11th-Mario-Triola/dp/… I also checked the 12 edition which is presumably the current edition, way too expensive. Same material wrapped in a different cover = not worth it. Commented Aug 4, 2016 at 17:44 Are you interested in understanding probability theory/statistics or just using probability theory/statistics? You say "build from the ground up" and to me that means diving straight into measure theory. On the other hand, you might have never even taken a calculus class, which will make understanding what a probability density function is very difficult as, given a random variable$X:\Omega \to \mathbb{R}$it is defined as the Radon-Nikodym derivative of a probability distribution (an induced measure)$\mathbb{P}(X^{-1}(\omega))$with respect to$\mu$, the Lebesgue measure on$\mathcal{B}(\mathbb{R})\$. For basic statistics, this is unnecessary but for a deeper understanding and for some applications, it is VERY necessary. Can you elaborate on your background/goals?