3 Irish?

Question:

How can someone be 1/3 of a particular ancestry? ex. I'm 1/3 Irish?

Can it happen perhaps through Grandparents and Great-Grandparents?

Best Answer - Chosen by Asker: Like This...for example:
Great-Great-Great Grand Parents marry and have a son:
Mom is 100% Irish
Dad is 100% Scottish
Son=50% Irish and 50% Scottish

Son Marries woman who is 50% Irish and 50% English and has daughter who is your Great-Great Grand Parent:
Daughter=50% Irish, 25% Scottish and 25% English

Daughter marries 100% Irish man and has son who is your Great-Grandparent:
Son=75% Irish & 1/8 or 12.5% Scotish and 1/8 or 12.5% English

Son marries woman who is 100% English and has daughter who is your Grandparent.
Daughter = 33% or 1/3 Irish, 6.25% or 1/16 Scotish and 25% or 1/4 English

and so on........