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Solutions to problems below
Mind Stimulating Exercises
Raymond Smullyan (1978). What is the Name of this Book: Riddle of Dracula and Other Logical Puzzles. Prentice-Hall: Englewood Cliffs, 1978.
- A man was looking at a portrait. Someone asked him, “Whose picture are you looking at?” He replied: “Brothers and sisters have I none, but this man’s father is my father’s son.” (“This man’s father” means, of course, the father of the man in the picture.) Whose picture was the man looking at?
- What happens if an irresistible cannonball hits an immovable post? By an irresistible cannonball we shall mean a cannonball which knocks over everything in its way. By an immovable post we shall mean a post which cannot be knocked over by anything. So what happens if an irresistible cannonball hits an immovable post?
- Two men were being tried for murder. The jury found one of them guilty and the other one not guilty. The judge turned to the guilty one and said: “This is the strangest case I have ever come across! Though your guilt has been established beyond any reasonable doubts, the law compels me to set you free.” How do you explain this?
- Two American Indians were sitting on a log- a big Indian and a little Indian. The little Indian was the son of the big Indian, but the big Indian was not the father of the little Indian. How would you explain this?
- A man is 100 yards due south of a bear. He walks 100 yards due east, then faces due north, fires his gun due north, and hits the bear. What color was the bear?
- Two American coins add up to thirty cents, yet one of them is not a nickel. What coins are they?
- Those of you who know anything about Catholicism, do you happen to know if the Catholic Church allows a man to marry his widow’s sister?
- Those of you who are interested in questions of good grammatical usage, is it more correct to say the yolk is white or the yolk are white?
- A train leaves from Boston to New York. An hour later, a train leaves from New York to Boston. The two trains are going at exactly the same speed. Which train will be nearer to Boston when they meet?
- On a certain house, the two halves of the roof are unequally pitched; one half slopes downward an angle of 60 degrees and the other half at an angle of 70 degrees. Suppose a rooster lays an egg right on the peak. On which side of the roof would the egg fall?
- A certain street contains 100 buildings. A sign-maker is called to number the houses from 1 to 100. He has to order numerals to do the job. Without using pencil and paper, can you figure out in your head how many 9’s he will need?
- A certain snail takes an hour and a half to crawl clockwise around a certain race track, yet when he crawls counter-clockwise around that same racetrack it takes him only ninety minutes. Why this discrepancy?
- If an airplane crashes right on the border of the United States and Canada, in which country would you bury the survivors?
- A certain Mr. Smith and his son Arthur were driving in a car. The car crashed; the father was killed outright and the son Arthur was critically injured and rushed to a hospital. The old surgeon took a look at him and said, “I can’t operate on him; he is my son Arthur!” How do you explain this?