One of Mr. X, his wife, their son and Mr. X's mother is an Engineer and another is a Doctor.
1. If the Doctor is a male, then the Engineer is a male.
2. If the Engineer is younger than the Doctor, then the Engineer and the Doctor are not blood relatives.
3. If the Engineer is a female, then she and the Doctor are blood relatives.
Can you tell who is the Doctor and the Engineer?

You can tell who the Engineer is, but not the Doctor.

The son is the youngest, and is also a blood relation to all the others, so by (2) he cannot be the Engineer.

By (3), if Mr.X's mother were the Engineer, she and the Doctor would be blood relatives. But her blood relatives here are all male, and this would violate rule (1). So Mr.X's mother is not the Engineer.

By (3), if the wife were the Engineer, she'd be a blood relative to the Doctor, but her only blood relative here is the son, whose being the Doctor would require the Engineer to be male by (1). So the wife cannot be the Engineer.

The Engineer must actually be Mr.X.

Since the Engineer is male, rule (1) has no further consequences--the Doctor can be either male or female.

If the mother were the Doctor, rule (2) would be violated, so the mother is not the Doctor.

Rule (3) has no further effect, as the Engineer is not a female.

The Doctor could be either the wife or the son without violating any of the statements.

Posted by Charlie on 2003-08-25 09:18:50