I'm no expert by any stretch of the imagination but from what I can gather it doesn't work like that as the pups can swing towards one side of the cross rather than it being exact 50:50 (if you know what I mean?). So these pups could come out more on the bull side, or more on the grey side, or more like a collie than you'd expect from this cross....so I guess it depends on the individual pup. Don't see what difference the exact percentage makes to be honest.
But, like I say, I'm fairly new to all this, that's what I understand from what other more experienced people have said though.