J.R. references the fact that an outsider (Jeremy Wendell) will soon own 30% of Ewing Oil. Prior to the arrival of Jack Ewing, both J.R. and Bobby each owned 30%. Jack's newfound 10% came from 5% each from J.R. and Bobby. As such, Christopher's share (soon to be WestStar's share) after Bobby's death should be 25%, not 30%.