Four friends live in a small town. Their names are a, b, c and d. They are a policeman, a carpenter, a farmer and a doctor. One day, A's son broke his leg. A takes his son to see a doctor. The doctor has a sister who is C's wife. The farmer has never been married. He keeps many hens. B often goes to farmers' houses to buy eggs. The police can see C every day because they are neighbors. Excuse me, who is the policeman in A, B, C and D? Who is the carpenter? Who is that farmer? Who is the doctor?
Answer: First of all, you can determine C, "The doctor has a sister who is C's wife", so C is not a doctor; "The police can see C every day", so C is not a policeman; "The doctor has a sister who is the wife of C, and the farmer has never been married." C is married, so C is not a farmer. Push c is a carpenter. Secondly, make sure that A "A takes his son to see a doctor." So a is not a doctor; A is married, so he is not a farmer; Judging from C's carpenter status, A is not a carpenter, and finally A is a policeman. Then determine B, "B often goes to farmers' houses to buy eggs", so B is not a farmer, a carpenter or a policeman, and B is a doctor. Finally, it is obvious that Ding is a farmer.
There are 25 desks and 20 stools in the classroom. How old is the teacher? Options:
A. unable to calculate, no answer
B.25+20=45 years old
C.25-20=5 years old