Dear Pojo,

Which do you apply first, weakness or resistance, eg. I use Porygon's
conversion 2 against a rhyhorn and changed porygons resist. to Fighting, but
porygons weak. is Fighting. Say rhyhorn used horn attack. If you apply
resist. first, the attack would do 30 - 30, which is 0 then doubled is 0. If
you apply weakness first, the attack does    30 X 2, which is 60, then 60 -
30 is 30, knocking out porygon.

Alex  

According to the rulebook, you apply weakness, then resistence.  So, in this case, it will do 30.

Scott