• Isabella Margalith

Logic Puzzles

Updated: Mar 13

Test your mind power and prove you are kind of a genius! Attempting to solve logical puzzles is a great way to improve your problem-solving and logical thinking skills while having lots of fun at the same time!


1. You’re at a fork in the road in which one direction leads to the City of Lies (where everyone always lies) and the other to the City of Truth (where everyone always tells the truth). There’s a person at the fork who lives in one of the cities, but you’re not sure which one. What question could you ask the person to find out which road leads to the City of Truth?


2. A farmer wants to cross a river and take with him a wolf, a goat and a cabbage. He has a boat, but it can only fit himself plus either the wolf, the goat or the cabbage. If the wolf and the goat are alone on one shore, the wolf will eat the goat. If the goat and the cabbage are alone on the shore, the goat will eat the cabbage. How can the farmer bring the wolf, the goat and the cabbage across the river without anything being eaten?


3. There are three people (Alex, Ben and Cody), one of whom is a knight, one a knave, and one a spy. The knight always tells the truth, the knave always lies, and the spy can either lie or tell the truth. Alex says: “Cody is a knave.” Ben says: “Alex is a knight.” Cody says: “I am the spy.” Who is the knight, who the knave, and who the spy?


4. The “Monty Hall” problem was made famous when it appeared in Parade magazine’s “Ask Marilyn” column in 1990, and it was so counterintuitive it had everyone from high school students to top mathematical minds questioning the answer—but rest assured, the solution is accurate. Named for the Let’s Make a Deal game show host, the puzzle goes like this:

You are given three doors to choose from, one of which contains a car and the other two contain goats. After you’ve chosen one but haven’t opened it, Monty, who knows where everything is, reveals the location of a goat from behind one of the other two doors. Should you stick with your original choice or switch, if you want the car?


Answers:

1. The question will be: “Which direction do you live?”. Someone from the City of Lies will lie and point to the City of Truth; someone from the City of Truth will tell the truth and also point to the City of Truth.


2. First, the farmer takes the goat across. The farmer returns alone and then takes the wolf across, but returns with the goat. Then the farmer takes the cabbage across, leaving it with the wolf and returning alone to get the goat.


3. We know Ben isn’t telling the truth because if he was, there would be two knights; so Ben could be either the knave or the spy. Cody also can’t be the knight, because then his statement would be a lie. So that must mean Alex is the knight. Ben, therefore, must be the spy, since the spy sometimes tells the truth; leaving Cody as the knave.


4. You should switch. At the beginning, your choice starts out as a one in three chance of picking the car; the two doors with goats contain 2/3 of the chance. But since Monty knows and shows you where one of the goats is, that 2/3 chance now rests solely with the third door (your choice retains its original 1/3 chance; you were more likely to pick a goat to begin with). So, the odds are better if you switch.


Bonus Question:

The day before two days after the day before tomorrow is Saturday. What day is it today?


Answer: Friday. The “day before tomorrow” is today; “the day before two days after” is really one day after. So if “one day after today is Saturday,” then it must be Friday.


Puzzles taken from: https://parade.com/970343/parade/logic-puzzles


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