2009-03-21 Sat - The Bridges VI - West to East

Indeed! my family roots are a third polish (jewish), a third russian (jewish), (on my mums side) and a third Anglo-Saxon settler/Viking (on my dads side)

How do you compute this? You have two parents, four grandparents, eight great-grandparents, sixteen ... etc. Where is there a number divisible by three? Or have I missed something completely obvious? :)