Why did the woman go to see the doctor?Because she had some trouble with ______.

A woman had some trouble with her teeth, so she went to see the doctor. She felt great pains, so the doctor first asked some questions. One question was "How old are you?" " Well, "she answered, "I don’t remember, but I’ll try to think. "She thought for a minute and then said, "Yes, I remember now. When I married, I was 20 years old, and my husband was 30. Now my husband is 60, I know, and that is twice 30.
    So I am twice 20. That is 40, isn’t it?" The doctor laughed and did not say a word. Then the woman was leaving the hospital. The doctor told her that she was actually 50 years old.