I was adopted as a baby, now 46. I am to inherit $5 from my adopted parents. Am I entitled to an equal share?

Sounds like your parents did estate planning and decided to change what would have been the distributive amounts had they not done so (had they died "intestate").  If they had died intestate, you would share equally - the law sees no difference between adopted and natural children.  But a person is entitled to leave his or her property as he or she sees fit, and can give more to one child than another, but he or she needs to do estate planning in order to accomplish that.