Final answer:
In joint tenancy, when one co-owner dies, their share automatically goes to the surviving joint tenant(s).
Step-by-step explanation:
In the scenario described, Sam and Nancy took title as joint tenants for the store building they bought. Joint tenancy is a form of property ownership where co-owners have equal rights to the property. When one joint tenant dies, their share automatically goes to the surviving joint tenant(s). So, when Nancy died testate (with a valid will), Sam now owns the store fully as the surviving joint tenant.