Have you studied using RxPrep? The book itself was enough for me to conceptually understand the calculations as well as understanding the interpretation of the answers. If you can derive the answer, youtube has great links to help understand specific terminology and the overall meaning (risk factor meaning, absolute risk reduction, hazard ratios, so on and so forth).
The bread and butter for me was RxPrep and their online test banks (the test banks were spot on for me when it came to NAPLEX). YMMV