Monthly Archives: June 2018

Clocks and time

There are many, many puzzles about clocks and time. In the nineteenth century, both Henry Dudeney and Sam Loydd designed a number of them, and in a future post I may collect them.

1) Basics*/*****
Today I encountered this problem on twitter, posed by a teacher for his students in primary school. Whisper your solution in the ear of the teacher to enter the classroom.

2) Advanced***/*****

You can check your solution here

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


PluszleĀ® is the trademarked name of a new type of number puzzle I encountered in the book/magazine shop at The Hague CS. I didnt want to buy it, but today my wife bought me a copy. The rules for the puzzle are elegantly simple. The grid is filled with numbers, and you have to cross out numbers till the sum of the remaining numbers equals the numbers in the right and bottom margins.

1) 5×5 nr 1*/*****

2) 5×5 nr 2**/*****

3) 6×6 nr 2**/*****

Priced at 4,95 euro and containing 375 puzzles it doesn’t sound like a bad deal. The main problem seems to me that the first part of the booklet contains 3×3 and 4×4 puzzles. In my humble opinion, these could have been omitted. Just this morning I was tweeting about education, automation of arithmetic, and differentiation in exercises for different students. Maybe I would have loved it to get puzzles like these at primary school as extra exercises.
The booklet is produced by Pluszle BV in Leusden, and outsider in the Dutch puzzle magazine world, which is dominated by Denksport and Sanders puzzels. Their website at mentions apps for the I-store and the android store, but I must admit I didn’t try the app.

Another, albeit smaller problem, is that the main variation is the size of the grids: the larger the more complex. It isn’t too difficult to create similar problems with multiplication:
4) 5×5 nr3*/*****

Another variation I can think of is a 4×4 grid with subtraction: cross out two numbers in every row and column so that the difference is the number in the right or bottom margin.

There is an even more puzzling form, but I think I reserve that for a subsequent post.

Now my words above may sound like a negative judgment, but I do not intend them to be that way. The larger sizes 6×6 and above, do offer a fair agree of difficulty.

Solution strategies
There are several solution strategies, here are the main ones:

(a) 8 can not be there, >5
(b) 3 can not be there, not in any combi
(c) 6 must be there, else you can not add up to 15
(d) all numbers must be there


When I got geography at primary school the main things I remember is that I had to learn which provinces we had in the Netherlands, and which towns are located where. At secondary school, the scope was broadened to Europe, the rest of the world. Of course, the location of major mountain ranges and rivers was included, again the form of “What is the name of this mountain range?” or “Where is river X?”.

This weeks puzzle is not so much a puzzle as an alternative geography test. If you are a geography buff, try your hand at this! The first question is a traditional question, to get you going, but the remaining questions require you to work with your geography knowledge in an unconventional way.

(Nearly) Everybody knows a lot more about the area close by than about countries far away. For this reason this questionnaire differentiates between USA, Dutch/European, and other countries. For these last, I welcome additions in the remarks section at the bottom of this post.

Rule: answer from your head – do not consult an atlas or wikipedia.

1) What is the capital of the State Arkansas?

2) Which states border the state of Missouri?

3) Mention three state capitals that start with the letter “D”.

4) Through which states does the river Rio Grande flow?

5) Which state has a larger surface: Wisconsin or Wyoming?

6) What is the largest (in terms of population) city in the state Alabama?

7) Which primary interstate highway serves the most states?

8) Geographical knowledge should also encompass knowledge not directly related to your home country. Which countries does Bolivia border in the west?

1) What is the capital of Ukraine?

2) With which countries does Austria share a border?

3) Mention 3 capitals starting with a B?

4) Through which countries does the river Donau flow?

5) Which country has a greater area, Austria or Czech republic?

6) Which capital has more inhabitants, Berlin, Londin or Paris?

7) Mention 5 countries in Europe with mountains above 3000 meters.

1) What is the capital of Cambodia?

2) With which countries does Afghanistan share a border?

3) Mention 3 capitals starting with a “D”

4) Through which countries does the Mekong river flow?

5) Which country has a greater area, Thailand or Iraq?

6) Which capital has more inhabitants: Manila or Riyadh?

7) What is the length of the longest highway in China?

1) What is the capital of Noord Holland

2) Which provinces border Gelderland?

3) Noem 3 steden met meer dan 100.000 inwoners die met de letter D beginnen

4) Door of langs welke provincies stroomt de rivier de Maas?

5) Welke provincie heeft een groter oppervlak: Drenthe of Limburg?

6) Welke stad in Gelderland heeft de meeste inwoners?

7) Door welke provincies loopt de A4?

You can check your solution here

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

Plastic snake

Last week I purchased another snake. It is not the first one I obtained, and if its price wasn’t ridiculously low at 4 euro, it would have remained in the shop at The Hague (or was it Utrecht?) Central station. The producer is listed as Clown Games.

You can read about the previous one here.

The packaging consisted of plastic, which I had to cup open.

At 4 euro it was so cheap that wondered if it would fall apart before i finished the booklet with examples, but it actually turned out to be sturdy, and even to a degree where it requires some force to turn.

The little instruction leaflet contained just 4 figures:

These can indeed be constructed:

There are numerous figures one can make with the snake. Credits for the following figures mostly go to my wife Jos and our daughter Margreet: