Nerd Battle

So, I got into a full fledged war at an auto parts store. We have English grammar to blame for the blood shed. I was picking up some oil, and saw a sign that read: Oil X or Oil Y and Filter Z $Price A. I glanced over the ad and emphasized the OR, assuming (surprisingly) that I could get the good price without buying the filter. Not logical, but that's how I read it!My purchase rang up full price....