Hey,
Thank you very much.
To be honest i wasn't concerned for the formulas because in comparison to University Engineering these are straight forward and intuitive if you understand the thought process behind them. For me it was more about having access to focussed practice questions with an explanation for their application. I also liked having a conclusive summary of what you are expected to know as not all are stated in the PMBOK.
Hope this helps, and as with any "maths" type skills practice is key.