Two old friends meet by chance, in the street.
They have not seen each other for twenty years.
The last time that they saw each other was when they were both 16 years old.
The first friend said: "I'm married but have no child, and you ?"
The second friend said: "I'm also married and have three girls."
The first friend asked: "How old are your three girls?"
The second friend said: "If you multiply their ages, you'll obtain my age!"
The first friend replied: "But I don't have enough clues to find their ages."
The second friend said: "Well, the sum of their ages equals the number of this house."
The first friend replied: "I'm sorry, but I still can not tell for sure..."
The second friend said: "The oldest girl is at the swimming pool."
The first friend replied: "Oh yes, now I know their ages."