(a) Effect. In all actions and proceedings not otherwise provided for by statute or by these rules, a presumption imposes on the party against whom it is directed the burden of proving that the nonexistence of the presumed fact is more probable than its existence.
(b) Inconsistent Presumptions. If presumptions are inconsistent, the presumption applies that is founded upon weightier considerations of policy. If considerations of policy are of equal weight neither presumption applies.