Transum Software

Trafalgar Square

Solve the number puzzles drawn on the pavement of Trafalgar Square in London.

In London's Trafalgar Square a young man from Slovakia captures the interest of passers-by with puzzles he's drawn with chalk on the pavement.

Chalk drawn puzzles

Above the puzzles were the only instructions:

Trafalgar Square Instructions

When I returned the following week all nine levels were ready for the keen puzzle solvers.

Trafalgar Square Puzzles

Can you explain how to find the missing number in each of the grids in the photograph above? The first few levels are quite easy but then it gets difficult. The answers are available lower down this page for subscribers (except the answer to level 8 which I'm still trying to figure out).

There are some easier 'Trafalgar Square' grids below for you to complete. They contain fixed rules but randomly-generated numbers. You can see how well you are doing by clicking the check button as often as you like as you work through the levels. If you get a level wrong try again:

Level 1


Correct Wrong

Level 2


Correct Wrong

Level 3


Correct Wrong

Level 4


Correct Wrong

Level 5


Correct Wrong

Level 6


Correct Wrong

Level 7


Correct Wrong

Level 8


Correct Wrong

Level 9


Correct Wrong


Do you have any comments about this exercise? Can you do level 8 in the third photograph on this page? Do you enjoy working on the puzzles on the Transum website? Please let me know by entering a comment here.


Lemon Law

Lemon Law

Change the numbers on the apples so that the number on the lemon is the given total.

The short web address is:


Nine Digits

Nine Digits

Arrange the given digits to make three numbers such that two of them add up to the third.

The short web address is:




Place the numbers one to nine in the table so they obey the row and column headings.

The short web address is:


The creators of the Trafalgar Square puzzles have made contact and kindly provided the photographs below:

Kardos photograph 1

Peter Kardos and Daniel Kardos, creators of the Trafalgar Square puzzles

Kardos photograph 2 Kardos photograph 3 Kardos photograph 4

This web site contains over a thousand free mathematical activities for teachers and pupils. Click here to go to the main page which links to all of the resources available.

Please contact me if you have any suggestions or questions.

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Mathematicians are not the people who find Maths easy; they are the people who enjoy how mystifying, puzzling and hard it is. Are you a mathematician?

Comment recorded on the 12 July 'Starter of the Day' page by Miss J Key, Farlingaye High School, Suffolk:

"Thanks very much for this one. We developed it into a whole lesson and I borrowed some hats from the drama department to add to the fun!"

Comment recorded on the 2 May 'Starter of the Day' page by Angela Lowry, :

"I think these are great! So useful and handy, the children love them.
Could we have some on angles too please?"

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Featured Activity

Beat The Clock

Beat The Clock

It is a race against the clock to answer 30 mental arithmetic questions. There are nine levels to choose from to suit pupils of different abilities.


There are answers to this exercise but they are available in this space to teachers, tutors and parents who have logged in to their Transum subscription on this computer.

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Go Maths

Learning and understanding Mathematics, at every level, requires learner engagement. Mathematics is not a spectator sport. Sometimes traditional teaching fails to actively involve students. One way to address the problem is through the use of interactive activities and this web site provides many of those. The Go Maths main page links to more activities designed for students in upper Secondary/High school.


If you found this activity useful don't forget to record it in your scheme of work or learning management system. The short URL, ready to be copied and pasted, is as follows:

Alternatively, if you use Google Classroom, all you have to do is click on the green icon below in order to add this activity to one of your classes.

It may be worth remembering that if should go offline for whatever reason, there are mirror site at that contains most of the resources that are available here on

When planning to use technology in your lesson always have a plan B!

Andy, USA

Saturday, August 18, 2018

"Only levels 1-7 seem to have a linear solution (ax + by + c = z) and are easily solved. What are the solutions to levels 8 and 9?"

Cesire Creamat, Twitter

Friday, September 14, 2018

Daniel Kardos, Slovakia

Tuesday, September 25, 2018

"Hi there,
I just found out that you uploaded those square puzzles from Trafalgar square as owner of those puzzles I found it interesting in here and I really like the idea . I solved your puzzles also. If you liked my puzzles and like to entertain people I could send to you few via email. Ps: To level eight in my puzzles- you all should think bit differently."

John, Transum

Wednesday, September 26, 2018

"Hey Daniel, thanks so much for getting in touch. It was so good to see your number puzzles in Trafalgar Square. It was funny that the first time I saw your work only the first four levels had been completed. I went back the following, rainy day but the rain had made a good job of washing the chalk away so I went back a week later when I got to meet you and take the final photograph. Nobody has solved level 8 yet so it must be quite different to the rest of the levels. It would be great for you to provide more puzzles that I could include on this website. I wish you many more sunny days in Trafalgar Square. Best wishes."

Pete Davies, Blackpool

Tuesday, October 2, 2018

"For level 8. First column - second column then add 12. Took me a while! Love problems like these. Will definitely use.

[Transum: Thanks Pete, good try, but that's not the puzzle that has foxed everyone. It's the Level 8 in the THIRD PHOTOGRAPH, drawn in chalk on the pavement of Trafalgar square that we can't work out. Please share if you manage to solve that!]"

Peter Davies, Blackpool

Tuesday, October 2, 2018

"Hi. Can you tell me what the first number in the second row is for level 8 on the pavement? It is not clear on the photo. Possibly why it is challenging if people not using the correct number. Many thanks.

[Transum: Hello Pete, really pleased to know that you are joining the search for the solution to level 8 in the third photograph. It's not obvious is it? here are the numbers in the puzzling square grid:


Good Luck]"

Peter Davies, Blackpool

Wednesday, October 3, 2018

"Thinking outside the box!. For level 8 the first row numbers are in base 2. All other numbers are in base 10. If we convert the base 2 numbers to base 10 then add vertically, the missing number is 8. Hopefully correct this time!

[Transum: Your idea doesn't work adding horizontally.]"

Anil, India

Friday, December 7, 2018

"The Trafalgar Square puzzles were very tough beyond Level 3."

Corinne Brooks, Birmingham

Friday, April 24, 2020

"Nimber 8 on Trafalgar Square is -141. Simple to work out using simultaneous equations."


Tuesday, December 1, 2020

"Hi there,
I have figured out #8 but do not know how to do #9 from the Trafalgar square questions. I would appreciate a hint."

Do you have any comments? It is always useful to receive feedback and helps make this free resource even more useful for those learning Mathematics anywhere in the world. Click here to enter your comments.


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Description of Levels



Exam Style questions are in the style of GCSE or IB/A-level exam paper questions (worked solutions are available for Transum subscribers).

More on this topic including lesson Starters, visual aids, investigations and self-marking exercises.

Answers to this exercise are available lower down this page when you are logged in to your Transum account. If you don’t yet have a Transum subscription one can be very quickly set up if you are a teacher, tutor or parent.

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You may also want to use a calculator to check your working. See Calculator Workout skill ##.

Don't wait until you have finished the exercise before you click on the 'Check' button. Click it often as you work through the questions to see if you are answering them correctly. You can double-click the 'Check' button to make it float at the bottom of your screen.

Answers to this exercise are available lower down this page when you are logged in to your Transum account. If you don’t yet have a Transum subscription one can be very quickly set up if you are a teacher, tutor or parent.

Log in Sign up