The documentation in the function wizard for the PROB function says "discreet" instead of "discrete" in the en-US version. Pretty sure there's nothing too secret about the calculation...
Kevin Peng committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/core/commit/?id=eccc5f97ba245faadf61cf4577b21d4f8da6460d fdo#52293 Changed "discreet" to "discrete"