Final answer:
Mary's symptoms such as memory loss, word substitutions, and disorientation suggest she is likely suffering from Alzheimer's disease, a condition characterized by severe cognitive decline.
Step-by-step explanation:
Mary, an 82-year-old with memory issues and unusual behavior, is likely suffering from Alzheimer's disease. This condition is characterized by disruptive memory loss, confusion about time or place, difficulty with planning and executing tasks, poor judgment, and personality changes. The description of Mary's symptoms, such as forgetting to pay bills, substituting words, and becoming disoriented, align with these key indicators of Alzheimer's. It's important to note that while some of these symptoms may occur in normal aging, the severity and impact on daily life suggest a more serious cognitive decline.