Value increases

[JMISBEST]

In my last Pirates of Drinax Campaign I decided to make 2 Portfolio Event Rolls for the same Pc and strangely enough the 1st was A 10+4 that would increase 1 of The Pcs Portfolio Items by +40% and the 2nd was A 4+3, which should have dropped the same Portfolio Items Value by -30%. and to be fair I ruled that the 2 rolls cancelled each other out and that their was A 50/50 chance for it to increase the items value by 1D2x5%, which was successful and netted it +10%, but now I'd like the opinion of the people on this website who, as far as I am aware, are at worst as good as me of what me and others should do if this happens to me or others. Please advise

 

[steve98052]

Plus 40% is equal to times 1.4, minus 30% is times 0.7, and plus 10% is times 1.1. Multiplying that out is times 1.078, or plus 7.8%

The lazy math way to do it is to add the percentages, +40% -30% +10% or +20%, but that's wrong unless the rules explicitly say that's how it's supposed to be done.