Elemental Blast (Sp): At 9th level, you can unleash a blast
of elemental power once per day. This 20-foot-radius burst
does 1d6 points of damage of your energy type per sorcerer
level. Those caught in the area of your blast receive a Reflex
save for half damage. Creatures that fail their saves gain
vulnerability to your energy type until the end of your next
turn.
Vulnerability means the creature
takes half again as much (+50%) damage as normal from that energy type, regardless of whether a saving throw is allowed or if the save is a success or failure.
What if the target has Energy Resistance?
Lets say Biggs the fire sorcerer uses Elemental Blast on wedge who has energy resistance 10 fire. The next round Biggs blasts Wedge with burning hands for 20 damage. Would it be 20 damage - 10 for resistance +10 for a total of 20 damage? And in that order? (thats how i understand it)
lets take it a step further
Lets say Biggs the fire sorcerer uses Elemental Blast on wedge who has energy resistance 20 fire. The next round Biggs blasts Wedge with burning hands for 15 damage. Would it be 15 damage - 20 for resistance, reducing it to 0 then 7 damage total? Remember "Vulnerability means the creature takes half again as much (+50%) damage as normal from
that energy type." OR would he only take 2 damage?
the right order of things here are
1 role damage in your example thats 20 points
2 add the +50% for a total of 30 fire dmg
3 aply resistance (10) and the target suffers a total of 20 dmg