You may just inherit 10% of that grandparent's DNA or you may inherit 30% or a bunch of other combinations.
I think it is all fascinating. But I am a little freaked out about it and I have not been tested.
Here is a fun comparison. These results are from 2 full siblings who are relative of mine.
#1 Europe-West 16%, Ireland 35%, Scandinavia 24%, Europe-East 8%, Great Britain 9%, Eastern Europe/Jewish 0%, West Asia/Middle East 0% South Asia/India 0% Iberian Peninsula 5% Caucasis 3% Italian/Greek 0% Africa 0%
#2 Europe-West 36%, Ireland 27%, Scandinavia 13%, Europe-East 12%, Great Britain 6%, Eastern Europe/Jewish 0%, West Asia/Middle East 3% South Asia/India 0% Iberian Peninsula 0% Caucasis 0% Italian/Greek 0% Africa 1%
Oh and I should add we have researched the family tree for those two siblings extensively and there is no one from Scandinavia that we are aware of. Even though it shows up in their results as 24% / 13%.