As you said, Khan academy is a great source to learn probability and statistics concepts. (I have followed their linear algebra materials and it was very helpful to visualize problems). In addition to that, if you are looking into solving more problems by hand to reinforce already built concepts, you can try the following book:
Schaum’s Outline of Probability and Statistics by John Schiller, Alu Srinivasan and Murray Spiegel
Also, I found a hackerrank tutorial challenge on statistics a lot of fun to do. It is a 10 day tutorial that has some easy coding challenges and multiple choice questions on distributions, centrality measures and so on. Following is the link:
Hackerrank - 10 days of statistics
If you are looking for Python/R specific tutorials on probability & stats, you can try the dataflair website. Following is the link for the Python - stats tutorials:
These are not mandatory, but just some resources that I have found useful to learn and apply concepts. You can pick and choose as to which area you wish to develop.
I hope you find some/all of them useful. Good luck!