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

Alice and the sweets

This week we have an honoured guest – Alice. Yes, Alice from Alice in Wonderland!
Alice heard Tweedledum say: Yesterday we got a number of wine gums. We both got the same number, but we played a game which I won and then I had 5 times as many wine gums as Tweedledee. But when I gave him one of my wine gums, I had only 4 times as many wine gums as he had.

This week we have an honoured guest – Alice. Yes, Alice from Alice in Wonderland!
Alice heard Tweedledum say: Yesterday we got a number of wine gums. We both got the same number, but we played a game which I won and then I had 5 times as many wine gums as Tweedledee. But when I gave him one of my wine gums, I had only 4 times as many wine gums as he had.

1) How many wine gums did Tweedledee and Tweedledum have?

That’s strange, Alice said. Yesterday, I mean the day before I fell into this rabbit hole, I had been playing a game with my sister. We were playing for matches, and after the game I had 7 times as many matches as my sister. But when I gave her one of my matchsticks, I had only 6 times as many matches.

2) How many matches did Alice and her sister have?

I was telling the story above to a little girl called Alais. Alais thought for a moment, then told me: That is strange. Yesterday, the day before you told me this puzzle, I was playing a game with my little sister. After the game, I had 10 times as many gumdrops as she had. Of course I gave her one, and then I had exactly 9 times as many as she had.

3) Alais is obviously a very smart girl. I knew she had had some elementary algebra at school. She had obviously figured out that there are an infinite number of numbers with which this puzzle can be told. Can you explain why?

You can check your solution here

New puzzles are published at least twice a month on Fridays. Solutions are usually published after one or more weeks.

100 doors challenge

Our daughter Margreet installed the “100 doors challenge” on her phone, and this weeks puzzles is based on one of the levels.

If 178 gives 237, what does 640 give?

You can check your solution here

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

Pattern code circle-square-triangle

What letter combination goes to the question mark?

If you like this puzzle, the good news is that you can find more puzzles like this one in my book.

Matchsticks – 3-7=8?

1) 3-7=8?^***/*****
Please correct the following equation by moving one matchstick:

1) 3-7=8?^***/*****
Please correct the following equation by moving exactly two matchsticks:

You can check your solutions here

Originally I had only puzzle nr. 2. I’d like to thank reader Mr. Haubrich for pointing out nr 1.

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

It’s just chance – or is it?

Searching for puzzle apps on my android phone, I encountered “Probability puzzles” by “atorch”. Nice puzzles, although this type of puzzle never was one of my favorites and probably never will be. The app is working well, and the puzzles are varied. Well recommended.

Probability actually has its root in betting and games of chance. I was reminded of this when I was downloading the “Print and play” game Fazenda. Unfortunately the dice were missing.
In the rules of Fazenda, there are three dice. All 18 sides are either brown or blue.

Three dice^**/*****
This weeks problem is this
Suppose that the three dice are identical, and that they each have 2 brown and 4 blue sides, what is the chance that at least two brown sides come up?

New puzzles are published at least twice a month on Fridays. Solutions are published after one or more weeks. You are welcome to discuss difficulty levels, variations and alternate solutions, but plz. don’t publish the solutions. The solutions will be published after one or more weeks, and yes, we know that you are smarted than any one else.

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.

Maze with numbers

This week I’d like to present a new type of maze.

Somewhere among the concept of this blog is a concept about mazes, their history, their shapes and their applications. In my small library are at least two good books about mazes. But here’s a new type of maze. Smaller versions may be suitable in the class room, while this shape and size are aimed at adults.

Your task? You see the two big 7’s? Find your way from one to the other, by moving vertically or horizontally, through squares which are a multiple of 7. Sounds easy, does it?

Here’s your exercise:

You can check your solution here

New puzzles are published at least twice a month on Fridays. Solutions are published after one or more weeks. You are welcome to discuss difficulty levels, variations and alternate solutions, but plz. don’t publish the solutions.

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.

Knights tours

Today we have “special forces”, such as the SAS in the UK, the Russian Spetsnaz, and the USA Rangers and Seals. In the middle ages these special forces had a name that still rings today: knights. The link between them and today’s puzzle is very thin: the knight got a place in western chess, and today’s puzzle uses the move of the knight on the chessboard.

In the series on new magazine format puzzles, I published a post on a new word format puzzle I encountered in the free newspaper metro in my native Netherlands.

In it, you have a 3×3 grid, the center of which is empty, while the outer edge is filled with letters. The letters form a word, and consecutive letters are always a knights jump (knight in chess) apart. Example:

For those who don’t know how a knight in chess moves: move one horizontally or vertically, followed by a diagonal move away from the starting square.

A knight on the square marked “K” may move to any square marked “X”.

My main criticism is that the puzzles as published by Metro are too easy to solve.

Today it occurred to me that the size of the board can be increased, and the size altered, to increase the difficulty of the puzzles.

9 letters^**/*****

12 letters^***/*****

20 letters^****/*****

That increased size raises the difficulty level of the puzzle is easy to understand: a larger size does not only give more starting positions, but also more possible moves on subsequent moves.
Another way to increase the difficulty is by not using single letters – the human mind in the western world is used to work with them – but digrams (two letter combinations) or trigrams (three letter combinations).

Proverb split into digrams^***/*****

Proverb split into trigrams^***/*****

A new puzzle is published at least twice a month. I welcome your comments below, but please do not spoil the fun for next visitors by listing your solutions. Solutions are published one or more weeks later. You can find more puzzles with words by following the link to the right.

You can check your solutions here