Category Archives: Logic

Bongard problem 36


Which rule satisfies the 6 figures on the left but not the 6 figures on the right?


The Russian scientist M.M. Bongard published a book in 1967 that contains 100 problems. Each problem consists of 12 small boxes: six boxes on the left and six on the right. Each of the six boxes on the left conform to a certain rule. Each and every box on the right contradicts this rule. Your task, of course, is to figure out the rule.

You can check your solution here

You can find more Bongard problems here and at Harry Foundalis site, and in the category ‘Bongard problems’ in the right margin of this page.

New puzzles are published at least twice a month on Fridays. Solutions are published after one or more weeks. You are welcome to remark on the difficulty level of the puzzles, discuss alternate solutions, and so on. Puzzles are rated on a scale of 1 to 5 stars.

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Bongard problem 35


Which rule satisfies the 6 figures on the left but not the 6 figures on the right?

The Russian scientist M.M. Bongard published a book in 1967 that contains 100 problems. Each problem consists of 12 small boxes: six boxes on the left and six on the right. Each of the six boxes on the left conform to a certain rule. Each and every box on the right contradicts this rule. Your task, of course, is to figure out the rule.

You can check your solution here

You can find more Bongard problems here and at Harry Foundalis site, and in the category ‘Bongard problems’ in the right margin of this page.

New puzzles are published at least twice a month on Fridays. Solutions are published after one or more weeks. You are welcome to remark on the difficulty level of the puzzles, discuss alternate solutions, and so on. Puzzles are rated on a scale of 1 to 5 stars.

River crossing


In the past I published several posts on river crossing puzzles. I think together they are the most extensive resource on river crossing puzzles on the web.

I used the week between Christmas and New Year to look for apps. To my surprise, there was just one, and it held just a few puzzles. Well, it did in spire me to:

1) The Autists and the Lazy.
Six people want to cross a river. They have a boat which can hold only 2 people at a time.
* Two of the six people are autists. They don’t want to be in the boat with any one else, though they don’t mind being on the same shore.
* Two of the people are outright lazy, and don’t want to row.
* The remaining two people are normal.
How many crossings does the boat have to make?

You can find the old posts here:
* Man, wife and kids – river crossing 1
* The farmer, the wolf, the goat and the cabbage – 2
* Three couples – river crossing – 3
* Bigamists – river crossing – 4

New brainteasers are published twice a month on Fridays.

You can check your solution here

In the bar with Truth-speakers, Switchers and Liars



The remote island of Zwrazr in the Logico archipelago is inhabited by three types of people: Truth-speakers, Liars, and Switchers. Truth-speakers always speak the truth, Liars always lie, and Switchers alternate their sentences between a true sentence and a lie.

After the previous puzzle you are thirsty, and the truth-speaker brings you to a bar close to the harbor. He points at a table with three people, and tells you they are a Truth-speaker, a Liar and a Switcher. He tells you the three people are called Al, Bill and Cindy.
Al says:
Bill is a Liar
Cindy is a Liar

Bill tells you:
Al is a liar
Cindy is a switcher

Cindy sips her cola and thoughtfully says:
Bill is a truth-speaker.

So, who is who?

You can check your solutions here

New puzzles are published at least twice a month on Fridays.

Truth-speakers, Switchers and Liars at the table in the restaurant


In the restaurant***/*****
The remote island of Zwrazr in the Logico archipelago is inhabited by three types of people: Truth-speakers, Liars, and Switchers. Truth-speakers always speak the truth, Liars always lie, and Switchers alternate their sentences between a true sentence and a lie.

In a restaurant, a group of natives are sitting at a circular table.
They take turns to say: the person to my left is a Switcher.
After that, they take turns, starting with the same person, to say: the person to my left is a Liar

What can you say about their type? How many are Truth-speakers? How many are Switchers? How many of them are Liars?

You can check your solution here

New puzzles are published at least twice a month on Friday. You are welcome to remark on the difficulty level of the puzzles, discuss alternate solutions, and so on. Puzzles are rated on a scale of 1 to 5 stars.

Bongard problem colours


The Russian scientist M.M. Bongard published a book in 1967 that contains 100 problems. Each problem consists of 12 small boxes: six boxes on the left and six on the right. Each of the six boxes on the left conform to a certain rule. Each and every box on the right contradicts this rule. Your task, of course, is to figure out the rule.

Bongard problem colours**/*****

You can check your solution here

You can find more Bongard problems here and at Harry Foundalis site, and in the category ‘Bongard problems’ in the right margin of this page.

New puzzles are published at least twice a month on Fridays. Solutions are published after one or more weeks. You are welcome to remark on the difficulty level of the puzzles, discuss alternate solutions, and so on. Puzzles are rated on a scale of 1 to 5 stars.

Next month I intend to publish a Christmas special.