AP Statistics question

<p>How do you calculate the quartiles? Stats seems to vary a lot from what I studied in the Indian Secondary Certificate course :( Like the variance thing. I heard AP uses /n-1 instead of /n
I'm so confused.
Also, can someone tell wether the following guides are reliable?(I have no hard books to study AP, so need to take free online prep)-
AP</a> Statistics Tutorial: Graphical Display of Data
Holloman's</a> AP Statistics | Notes
AP</a> Statistics Notes Ms
Table</a> of Contents</p>

<p>Thanks!</p>