My paternal great grandfather was Chinese from China married my paternal Great grandmother who was Chamorro. They gave birth to my paternal grandfather. This makes my paternal Grandfather 1/2 Chinese 1/2 Chamorro. My paternal grandfather married a Chamorro woman and gave birth to my father. What does that make my Dad? My Dad married my mother who was Chamorro and gave birth to me..What does that make me?
By my calculation ...
Your paternal grandfather is 50% Chamorro and he married a 100% Chamorro woman so their offspring are 75% Chamorro i.e. (50% + 100%) / 2.
One of those offspring was your 75% Chamorro father who married another 100% Chamorro woman and so their offspring (including you) are 87.5% Chamorro i.e. (75% + 100%) / 2.