Question

Introducing Mary to her friend Anne, Katy said 'Her mother is the only daughter of my father". Who is Katy to Mary?

Answer 1

Mother

Explanation:

Refer to diagram if needed:

Mary's mother's father is the same person as Katy's father.
Therefore, Katy and Mary's mother must be siblings or in the same generation. However, Katy must be the same person as Mary's mother as Mary's grandfather only had one daughter, so Katy is Mary's Mother