I ask about percentage, because by such I have an equivalent percentage as if a grandparent was actually born there.  The work out is as follows:  2 Great-Grandparents from Ireland=100% Irish grandmother=50% Irish parent=25% Irish me.  Where as if 1 grandparent from Ireland=50% Irish parent=25% Irish me.  Either way I work out to be the same percentage heritage.
I realise that in general that great-grandparents are considered to be too distant, however there is a major difference between 1 great grandparent ergo a 50% Irish grandparent and so on, and a 100% Irish grandparent...
Hellllllllllllllooooooooooooo Brendan
What’s with this adding up percentages ….. WHY would you add up percentages?
You have 
2 parents     2/2 = 100%
4 grandparents  4/4 = 100% 
8 great grandparents 8/8 = 100% 
I think your Matherickings are a bit 'double dutch' to me  
 2 /8 greats were Irish = 1/4 OF THAT GENERATION were Irish = 25% of THAT GENERATION  

Using your mathericking logickings and my fingers
4 grandparents = 12.5% Irish
2 parents generation = 6.25% Irish
I think you are 3.125 % Irish   

What about the other 96.875% 
Teddles