I'm looking at the skill formula and there seems to be a probleme (either with the formula or there's something I'm doing wrong). For the purpose of the test, lets say I'm an epic mage with 30 Int. and a Dex of 16 which is highly plausible. Said mage is trying to learn riding so he's puting his first rank.

100xp - (Int. x 5xp) + Current rank x (5xp - Ability mod.)

so it comes down to :
100XP - (30 x 5xp) + 0 x (5xp - 3)
100XP - 150XP + 0 x 2
100XP - 150XP = -50XP

So basicaly I gain xp from getting my first rank in riding?