am interested in quant analytics. hope statistics is heart for quant analysis. so, what are the best sources to learn core statistics (in depth) and what is the best approach to learn statistics?
Sheldon Ross - A first course in probability. Probability is the foundation of statistics so this is a good place to start
Cassela & Berger - Statistical Inference. This will give you a solid understanding of the ideas behind confidence/prediction intervals, hypothesis testing, all the way up to to linear regression.
Hogg -Intro to Mathematical Statistics. This is heavy on analytics. Good if you're comfortable with higher level math.
A good book on linear algebra so you can get a better understanding of how things are working under the hood. It's not strictly necessary but definitely helpful.
Those 4 will get you started but they're just the beginning.